So I played a BM66 at Pintastic17 that had one of the protectors on it. Thought it was a great idea and have since purchased a few for some of my machines.
On a new Machine with all the gadgets it can be overwhelming to disassemble the playfield to install but I think it's worth it. On older machines that you really like but has sunkin inserts and paint loss and don't want travel the new playfield swap road, this is an excellent alternative.
Without any doubt I feel the ball is faster on these protectors. Less friction is my thought as times I swear I have seen the ball slide instead of rolling.
I have no regrets buying and installing.
-Mike