So I bought one in the summer from CTC Supplies for a 10" A2 upper, and after about 50 rounds I noticed a crack and my rounds were being deflected 8 feet low at 50 yards. So I removed it, tried contacting Griffin Armaments directly, got no responses, BUT my friend has one on his 10.5" that works just fine, so I ordered a second one.
See that line around the rear of the compensator? That's a hairline crack that started with only 20 rounds fired.
I've already removed it and emailed CTC Supplies, now I'm waiting to see if they can get some answers from Griffin.