I just played the demo and I have to say it is quite charming. And it is a competent 3rd party shooter that looks and runs great, under the CachyOS Linux kernel. No, I don't have a 4-button mouse, but you can work around it by altering the default controls. Not the most ideal thing in the world, but it functions.
I would REALLY like to buy this on GOG. I've already bought a new mouse on Ebay just for the dual control capability, so I'm gonna play it real soon, one way or another.