I had been going under the assumption that since A1 had a rating it must have a walkthrough and I was just unable to find it.
For what it is worth I found A5 easier than this one - perhaps b/c I didn't see step 6 until the end.
Here is my walkthrough for Assassin 1. Not bothering with tiny text. I would rate this as 0.75.
Assassin 1 (the original) Walkthrough
Preliminaries
a. 10(2)n1 and n56 and n7 = {19/28/37/46} (no 5)
b. 9(3)n14 = {126/135/234} (no 7,8,9)
c. 15(2)n14 and n47 = {69/78} (no 1..5)
d. 6(2)n12 = {15/24} (no 3,6..9)
e. 17(2)n23 = {89} (no 1..7) -> 8,9 locked for r3
f. 7(2)n3 and n78 = {16/25/34} (no 7..9)
g. 4(2)n36 = {13} (no 2,4..9) -> 1,3 locked for c9
h. 11(3)n3 and n4 = {128/137/146/236/245} (no 9)
i. 9(2)n47 and n89 = {18/27/36/45} (no 9)
j. 8(2)n45 = {17/26/35} (no 4,8,9)
k. 12(2)n56 = {39/48/57} (no 1,2,6)
l. 21(3)n6 = {489/579/678} (no 1,2,3)
m. 13(2)n69 = {49/58/67} (no 2)
n. 5(2)n9 = {14/23} (no 5..9)
1. Innies Outies n3: r3c7 – r4c89 = 6
1a. -> r3c7 = 9; r4c8 = 2; r4c9 = 1
1b. -> r3c6 = 8
1c. -> r3c9 = 3
1d. -> r23c8 = [87]
1e. -> r34c1 = [69]
1f. -> r67c1 no 3
1g. -> r6c6 no 3
1h. -> r6c7 no 4
1i. -> r12c7 no 4
1j. -> r7c7 no 1
2. r4c34 = {78} -> locked for r4
2a. -> r4c67 = {46} -> locked for r4
3. Innie and Outie n1: r3c3 – r4c2 = 2
3a. -> r3c3 = 5; r4c2 = 3
3b. -> r3c4 = 1
3c. -> r4c5 = 5
3d. -> r23c2 = {24} -> locked for n1 and c2
3e. -> r1c3 no 8
3f. -> r6c3 no 7
3g. -> r6c4 no 3
3h. -> r6c7 no 7
3i. -> r23c5 = [72]
3j. -> r1c3 no 3
3k. -> r23c2 = [24]
3l. -> r1c7 no 5
3m. -> r7c3 no 6
3n. -> r7c4 no 2
4. killer pair {12} in c7 in 7(2)n3 and 5(2)n9
4a. -> r7c7 no 2
4b. -> r7c6 no 7
5. Innies and Outie n8: r7c46 – r6c5 = 3
5a. -> max r7c45 = 11 -> max r6c5 = 8 (no 9)
should have seen this much much earlier
6. Outies c12: r5c3 = 6
6a. -> r5c12 = [41]
6b. -> r5c34 = [26]
6c. -> r4c67 = [46]
6d. -> r6c5 = 1
6e. -> r7c46 = [31] (step 5a)
6f. -> r7c3 = 4
6g. -> r7c7 = 8
6h. -> r6c9 no 5,9
6i. -> r7c9 no 7
6j. -> r12c7 = [25]
6k. -> r56c7 = [73]
6l. -> r6c6 = 9
6m. -> r1c8 = 1
6n. -> r67c9 = [85] (4 blocked by r12c9)
singles and cage sums left.