Protection

one of us slips and hits the other one

Within the existing rules I would interpret the fouler to be the one who lost control of their bike/balance and caused the incident (otherwise players could feign losing control of their equipment whenever they liked to gain an advantage), not malicious, still a foul, unlikely to get called unless it changed the flow of the game.

Mallet to body is a foul but only gets called if someone is hurt so we should probably think about that part.

This is the crux, just because it's now "ok" to hit someone in the face cage (as there's no incident) I don't want there to be an underlying belief that mallet-to-face contact is allowed (or incidental), it's not allowed, players must keep their equipment in check (my opinion).

I worry about less experienced players not considering the risk or evaluating them incorrectly because they see the choice you have made based on your ability, bike handling and risk tolerance.

Again, this assumes your risk assessment (for newer players) is that it's safer to wear a face cage. I would advise them to wear a face cage if they were worried about losing teeth or getting stitches, but otherwise I believe they're safer with a plain old helmet (less likely to crash badly, more aware of their surroundings, etc). Controversial, yes.

At the very least I'd tell them to ride around with a face cage on (maybe do some chores at home) and get used to it before hitting the court (unprepared)... all the gear, no idea, etc.