I used the glass top for a short while but I no longer use it.. I don't think it would break.. it does keep the tank a degree or two cooler.. which isn't a big deal for me since i usually cool my place to the low 70s..
however, there is poor gas exchange with the lid on and it was making my pH low.
I don't think your concerns are a big deal. Yes, snails go into my filter bins.. they also come back into the display.. it really doesn't hurt anything for them to go back there.. in fact, if they go back there and stay there i figure there is algae back there they are eating. they never leave the tank because, well i don't have marine water outside of it
There are fish that are surely jumpers, but I haven't had my clown fish or blenny even look like they wanted to jump.. if they ever get stressed they are darting into the rocks, not out of the tank..
I would leave the top off, and then if you have problems, you can try to come up with an alternative..