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573 892 641
824 613 597
196 475 823
412 356 789
658 729 134
937 148 265
345 261 978
769 584 312
281 937 456

This is an optimised solution so some obvious eliminations are not included. However, I usually try and do the clean-up as I go, at the beginning anyway. Please let me know of any mistakes or clarifications.

Prelims
i. 8(2)r3c3: no 4,8,9
ii. 7(2)r3c4: no 7,8,9
iii. 12(2)r3c5: no 1,2,6
iv. 11(2)r3c6: no 1
v. 15(2)r3c7: no 1..5
vi. 11(3)n4: no 9
vii. 21(3)n6: no 1,2,3
viii. 10(3)n6: no 8,9
ix. 10(2)r6c5: no 5
x. 9(2)n7: no 9
xi. 14(2)n8: no 1..4,7
xii. two 11(2) cages in n8: no 1
xiii. 8(2)n9: no 4,8,9

1. "45" on c6789: 2 innies r25c6 = 12 (no 1,2,6)

2. "45" on c789: 3 outies r156c6 = 11 and must have 1 for c6
2a. = {128/137/146}(no 5,9)

3. 14(2)n8 = {59/68} = [5/6,5/8,6/9..]
3a. -> {56} blocked from both 11(2) cages in n8 (no 5,6)

Andrew will be relieved there is no killer quad in c4 this time! (see comment at the end of his WT for A219)
4. "45" on c1234: 2 innies r25c4 = 13 (no 1,2,3)
4a. {58} blocked by 14(2)n8 (step 3.)(no 5,8)
4b. = {49/67} = [6/9..]

5. Killer pair 6 & 9 in c4 in h13(2)(step 4b) and 14(2)n8(step 3.): both locked for c4
5a. no 1 in 7(2)r3c4

Lots of symmetry between the next step and step 2!
6. "45" on c123: 3 outies r167c4 = 11 and must have 1 for c4
6a. = {128/137}(no 4,5)

7. "45" on n8: 3 innies r7c456 = 9 and must have 1 for n8
7a. = {126} only: all locked for r7 & n8
7b. no 1,2,3,6,7 in r6c5
7c. no 9 in two 11(2) cages in n8

8. 14(2)n8 = {59} only: both locked for c4
8a. -> 7(2)r3c4 = {34}: both locked for c4
8b. and h13(2)r25c4 = {67} only: both locked for c4

9. "45" on n1: 2 outies r1c4 + r4c3 = 10 = [82] only
9a. r3c3 = 6
9b. r12c3 = 7 = {34} only: both locked for n1 & c3
9c. no 9 in r4c7

10. r67c4 = {12} = 3 -> r67c3 = 12 = {57} only: both locked for c3

11. "45" on n4: 2 remaining innies r6c13 = 16 = [97] only
11a. r7c3 = 5
11b. no 4 in 9(2)n7

12. 16(3)n4 = {358} only
12a. r5c3 = 8
12b. r56c2 = {35}: both locked for c2 and n4

13. "45" on c12: 1 innie r9c2 = 8

14. "45" on n9: 1 innie r7c7 - 4 = 1 outie r6c9
14a. r7c7 from (789); r6c9 from (345)

15. 9 in n6 only in 21(3) = {489/579}(no 6)

16. 1 in r4 only in n4: 1 locked for n4

17. "45" on r1234: 2 outies r5c19 = 10 = [64] only
17a. r4c12 = {14}: 4 locked for r4
17b. r4c89 = 17 = {89}: both locked for r4 and n6

Cracked.

I'll rate my walkthrough for A220 at 1.25, consistent with the SSv3.3.1 score, because I used a couple of CCCs. Ed's walkthrough probably gets a slightly lower rating.

Prelims

a) R34C3 = {17/26/35}, no 4,8,9
b) R34C4 = {16/25/34}, no 7,8,9
c) R34C5 = {39/48/57}, no 1,2,6
d) R34C6 = {29/38/47/56}, no 1
e) R34C7 = {69/78}
f) R67C5 = {19/28/37/46}, no 5
g) R89C1 = {18/27/36/45}, no 1
h) R89C4 = {59/68}
i) R89C5 = {29/38/47/56}, no 1
j) R89C6 = {29/38/47/56}, no 1
k) R89C9 = {17/26/35}, no 4,8,9
l) 11(3) cage at R4C1 = {128/137/146/236/245}, no 9
m) 21(3) cage at R4C8 = {489/579/678}, no 1,2,3
n) 10(3) cage at R5C7 = {127/136/145/235}, no 8,9

1. 1 in N8 only in R7C456, locked for R7
1a. 45 rule on N8 3 innies R7C456 = 9 = {126/135}, no 4,7,8,9, clean-up: no 1,2,3,6 in R6C5
1b. Killer pair 5,6 in R7C456 and R89C4, locked for N8

2. 45 rule on R12 2 innies R2C19 = 15 = {69/78}
2a. Min R2C9 = 6 -> max R3C89 = 6, no 6,7,8,9 in R3C89

3. 45 rule on R1234 2 outies R5C19 = 10 = [19/28/37]/{46}, no 5, no 7,8 in R5C1

4. 45 rule on R6789 2 innies R6C28 = 9 = {27/36/45}/[81], no 1,9 in R6C2

5. 45 rule on R89 2 innies R8C28 = 7 = {16/25/34}, no 7,8,9

6. 45 rule on N1 1 outie R1C4 = 1 innie R3C3 + 2, no 1,2,6 in R1C4

7. 45 rule on N3 1 innie R3C7 = 1 outie R1C6 + 6, R1C6 = {123}, R3C7 = {789}, clean-up: no 9 in R4C7
7a. 21(3) cage at R4C8 = {489/579} (cannot be {678} which clashes with R4C7), no 6, 9 locked for N6, clean-up: no 4 in R5C1 (step 3)

8. 45 rule on N6 3 innies R4C7 + R6C79 = 14
8a. Min R4C7 = 6 -> max R6C79 = 8, no 8 in R6C79

9. 45 rule on N7 1 outie R6C1 = 1 innie R7C3 + 4, R6C1 = {6789}, R7C3 = {2345}

10. 45 rule on N9 1 innie R7C7 = 1 outie R6C9 + 4, R6C9 = {12345}, R7C7 = {56789}

11. 45 rule on C1234 2 innies R25C4 = 13 = {49/58/67}, no 1,2,3
11a. Killer triple 4,5,6 in R25C4, R34C4 and R89C4, locked for C4, clean-up: no 2,3 in R3C3 (step 6), clean-up: no 5,6 in R4C3
[Ed commented “Andrew will be relieved there is no killer quad in c4 this time! (see comment at the end of his WT for A219)”. Only a killer triple this time! ]
[Oops! After going through Ed’s walkthrough, I noted that I’d missed the clash with R89C4 eliminating {58} from R25C4.]

12. 45 rule on C6789 2 innies R25C6 = 12 = {39/48/57}, no 1,2,6

13. 45 rule on C89 1 innie R9C8 = 1 outie R5C7 + 4, R5C7 = {12345}, R9C8 = {56789}

14. 12(3) cage at R8C7 = {129/138/147/237/246/345} (cannot be {156} which clashes with R89C9)
14a. R9C8 = {56789} -> no 5,6,7,8,9 in R89C7

15. 45 rule on N3 3 innies R123C7 = 19 = {289/379/568} (cannot be {469/478} which clashes with R34C7, CCC), no 1,4
[With hindsight, this 45 is good to eliminate the 1 but 45 rule on N3 2 innies R12C7 = 1 outie R4C7, IOU no 4 in R12C7 is a simpler way to eliminate the 4.]

16. 45 rule on N1 3 innies R123C3 = 13 = {139/148/157/247/256/346} (cannot be {238} because no 2,3,8 in R3C3)
16a. R12C3 cannot contain 5 because R13C3/R23C3 would clash with R34C3, CCC, no 5 in R12C3
[Similarly, with hindsight, 45 rule on N1 2 innies R12C3 = 1 outie R4C3 + 5, IOU no 5 in R12C3.]
16b. 15(3) cage at R1C3 = {168/249/267/348}
16c. 7,9 of {249/267} must be in R1C4 -> no 7,9 in R12C3
16d. R123C3 = {148/247/256/346} (cannot be {157} because 5,7 only in R3C3)
16e. 1 of {148} must be in R3C3 -> no 1 in R12C3

17. 45 rule on C123 3 outies R167C4 = 11 = {128/137}, no 9, 1 locked for C4, clean-up: no 7 in R3C3 (step 6), no 6 in R34C4, no 1 in R4C3
17a. 1 in C4 only in R67C4, locked for 15(4) cage at R6C3, no 1 in R6C3

18. 1 in C6 only in R167C6
18a. 45 rule on C789 3 outies R167C6 = 11 = {128/137/146}, no 5,9
18b. 4,7,8 of {128/137/146} must be in R6C6 -> no 1 in R6C6

19. R7C456 (step 1a) = {126} (only remaining combination), locked for R7 and N8, clean-up: no 7 in R7C5, no 8 in R89C4, no 9 in R89C5, no 9 in R89C6

20. Naked pair {59} in R89C4, locked for C4, clean-up: no 4,8 in R25C4 (step 11), no 2 in R34C4

21. R67C4 = {12} (hidden pair in C4), locked for 15(4) cage at R6C3, no 2 in R6C3
21a. 15(4) cage at R6C3 = {1239/1248/1257}
21b. 7,8,9 only in R6C3 -> R6C3 = {789}

22. R1C4 = 8 (hidden single in C4), R12C3 = 7 = {34}, locked for C3 and N1 -> R7C3 = 5, R6C3 = 7 (step 21a), R4C3 = 2, R3C3 = 6, clean-up: no 9 in R2C9 (step 2), no 9 in R3C6, no 4 in R4C5, no 3,5 in R4C6, no 4 in R5C6 (step 12), no 8 in R5C9 (step 3), no 2 in R6C8 (step 4), no 4 in R89C1, no 3 in R8C8 (step 5)

23. 45 rule on N4 1 remaining innie R6C1 = 9, clean-up: no 6 in R2C9 (step 2), no 1 in R7C5

24. Naked pair {78} in R2C19, locked for R2 -> R2C4 = 6, R5C4 = 7, clean-up: no 5 in R2C6 (step 12), no 5 in R3C5, no 4 in R3C6, no 3 in R5C1 (step 3), no 5 in R5C6 (step 12)

25. R5C4 = 7 -> R5C56 = 11 = [29/38/83], no 1,4,5,6,9 in R5C5

26. R6C4 = 1 (hidden single in N5), R7C4 = 2, R7C5 = 6, R6C5 = 4, R7C6 = 1, R34C4 = [43], clean-up: no 9 in R2C6 (step 12), no 9 in R3C5, no 7 in R3C6, no 8 in R4C5, no 8 in R5C56 (step 25), no 5,8 in R6C2, no 5 in R6C8 (both step 4), no 7 in R89C5

27. R25C6 = [39], R5C5 = 2, R12C3 = [34], R1C6 = 2, R3C7 = 8 (step 7), R4C7 = 7, R2C19 = [87], R3C5 = 7, R4C5 = 5, R3C6 = 5, R4C6 = 6, R6C6 = 8, R7C7 = 9, R6C7 = 2 (cage sum), R5C9 = 4, R5C1 = 6 (step 3), R6C2 = 3, R6C8 = 6, R6C9 = 5, clean-up: no 1,3 in R89C1, no 1,3 in R89C9

28. R5C23 = [58] (hidden pair in N4)

29. Naked pair {19} in R89C3, locked for N7, R9C2 = 8 (cage sum)

30. Naked pair {26} in R89C9, locked for C9 and N9

31. R2C9 = 7 -> R3C89 = 5 = [23], R3C12 = {19], R4C12 = [41]

32. Naked pair {27} in R89C1, locked for C1 and N7 -> R7C1 = 3, R7C9 = 8, R7C2 = 4, R7C8 = 7, R8C8 = 1 (cage sum)

and the rest is naked singles.