Rattan is great when you're in steel armor, but for most HEMA "Blossfechten", it's done with padding and a fencing mask/helmet, since it's unarmored combat that's being recreated. So something lighter hitting is ideal.
I think with the simulators we've used at VAF, the shinai are the only ones that haven't bruised me up so far. They certainly are capable of it, but they're also very controllable and make it easy to pull your hits.
We've migrated away from wooden wasters, and in our group aluminum never caught on. The aluminum doesn't really afford you anything over steel except maybe being cheaper (depending on who makes it). The aluminum blades have to be made fairly thick to get the right weight, which is fine in the sense that you want wide edges to be safe. However, it doesn't have the sort of flex that steel does, so they have no give at all. So you might as well use steel.
But yeah, any time you face off against an opponent, there's a certain amount of trust that must exist that you won't try to actually hurt each other. Accidents happen of course, since we are after-all trying to do a martial art. Injuries will happen. But if someone is being unsafe, careless, reckless, etc, it's perfectly fine to choose not to fight them.