I have these on about 15 tanks and love how lightweight and easy they are to just move out of the way when I need to.
When I first cut the pieces, I had an issue on my mbuna tank. The aquaclear filter clogged a bit while I was at work, somehow directed the flow straight to the back of the lid, which was open where it had been cut, and the water shot straight through it and out the front. Came home to a decent amount of water on the floor. I have since ran silicone along all of the edges that were cut. Learned my lesson there.