1. First time I installed it, it did move while practicing dummy loading. It was because I had only slightly tightened it. After that I tightened it down well and it hasn’t budged after many life fire training sessions and a match. I’m easily over 1000 rounds with it on. Make sure you tighten down the magazine tube cap first, and check that barrel is seated properly against receiver, before tightening set screws. Otherwise the front set screws will sit on the edge of the front mounting location.
2. They have not moved. They do leave a small “dimple” in the finish of the front set screws. Doesn’t bother me but it could bother some. I actually went and made a small recess with the Dremel, so that the set screws have a fixed location to grab.
3. I used blue loctite and it has worked well. Hasn’t loosened, and wasn’t an issue removing forend. I have removed it several times and haven’t had to reapply loctite yet.
Like many, I agree that it’s not a great setup with the set screws, but I do like the feel of the grip and Mlok feature. Until something better comes out, this has been doing the job well, despite having to use tools to strip down the shotgun.