I used these while doing some work for a company that was doing live broadcasts of players during arena football and minor league hockey games last year. The company had some sort of partnership with Quantum so they were given a bunch of transmitters and receivers.
The transmitters are pretty slim and actually somewhat flexible (like a hard rubber), wouldn't be too worried about a player landing on it and didn't receive any complaints about wearing them. Didn't have any break except a few mics at the connector.
We were using Countryman B6's that were wired with the Q5X connector (by Quantum), so I'd imagine you could use a variety of lavs with them, but don't recall if the connector was waterproof. I think they had tested trams and a couple other mics prior to settling on the B6's.
They worked well for the situation, the remote activation was pretty flawless - we wired up the players pads before the game, and were able to power them on from a distance once they took the field/ice and power off in between periods/quarters to save battery life. Q5X has a computer program to power them on and off, adjust gain and frequencies remotely, but it's Windows only.
The transmitters I used were the QT-1000 "player mics" and the receivers were the QR-2000 rack mounts. As far as I know they still don't have individual belt pack style receivers. Definitely a solid system, but geared more towards sporting events than anything else.