Just swapped out the OEM Sig grips on my M11-A1 with the E2 grips. Took roughly 3 minutes to complete. I ordered the Sig p229 E2 Grip Kit from Top Gun Supply (which arrived in two days). Since my M11-A1 already had the new de-cock lever I only had to make the changes to the hammer spring and strut.
If you've never removed that assembly, use a flat head screwdriver in the hole at the bottom of the hammer seat and push up. It's far easier than you might think.
Replace that assy with the new strut and seat and you're good to go. Some users have even said you don't need to swap out the hammer strut assy on the newer M11-A1s.