I was thinking that the group would be all rentals but they would at least all know each other - rather than just a Rental only day where strangers turn up - so it might make it a bit better, but then yea it might make it worse if they all know each other and take things too far.
Just trying to limit the potential for anyone being tempted to overshoot even with a semi only rule but yea I guess limiting it to mid/lo caps is really just trying to take away the marshalling responsibility which isn't great. Far better to let people use the equipment they prefer and then just enforce proper rules.
I'm thinking to keep things simpler I'd probably just for a 50/50 split of Firehawks / Raiders just so mags are interchangeable, both are pretty similar from a usability standpoint, but then there's still some "variety" just to give the rental players a bit of choice.
Definitely getting friendly with the competition is a good shout yea. In my day job we make games in a small niche market and we run a discord and have devs from other games in there too who make similar games and are technically "competition" but we encourage people recommending other games than ours etc as it all helps everyone.
Speaking of rental equipment, I'm obviously a long way off from this stage but just getting ideas of costs and trying to avoid doing the day job for a minute so I started looking around at face protection. All I want is something full face, to limit the potential of someone removing the bottom half, losing some teeth, and then blaming me, and probably not a helmet but maybe that'd be better, especially to accommodate glasses wearers.
But the closest I can find is one that has mesh eye protection. BBs are plastic and can shatter. Doesn't really mix that well with mesh.
https://www.defconairsoft.co.uk/product/big-foot-airsoft-mask-with-mesh-goggles/