The finger holes to take the boards out and move them for a twist are actually quite large. I happen to have some pretty large "Bear Paw" hands and my thumb fits into the slots very easily. Obviously if you have many pieces on the board they will slide around but that happens regardless of a board being used or not.
Having the board helps keep the dungeon itself in place which honestly was my only complaint with the game. I had a foam core board for a while but i found it so light weight that it moved a lot and messed things up. this board has the weight i wanted that keep it in place.
I was looking at the French plastic one (next few pictures) and thought it was amazing, but too cost prohibitive.
Your board looks great and maybe not that expensive. Would you consider making another for a fee? I have no access to woodworking material, nor the skills!