You don't want your mag releases covered, you want them exposed.
This for sure. While in a training class last month, I went to shoot my exercise and was surprised when the gun locked back after one shot, after being drawn from the holster with a full magazine. Looked down and realized the magazine was on the floor by my feet. The inexpensive kydex holster I picked up off of Amazon was great in every respect, except the mag release was covered on the back side and that was causing the mag release to be pressed occasionally. I've been carrying in another holster until I can pick up a dremel to remove enough material to take care of the problem.