It's not too bad. There can be a little bit of trickiness in figuring out the exact position of the hammer and it's return spring, but not bad. The Gray Guns video is a great help, as are the SIG-specific tools. I still need the video when I do it (unlike the Glocks), but that might just be because I've only detail-stripped the SIG 4 or 5 times, compared to dozens for the Glocks.
I hope that this new kit will work in the 225A (or a 225A version will be forthcoming)--I would love to drop one into an all-stainless 225A.