Yes, it should work fine connecting multiple engines to it.

Also this works fine with 2 engines right, like with the winterhalter? can i just connect two engines at once to it?

There is no easy way to tell if maintain position is engaged so it will.. While in my testing this was fine, I think you may see some oscillation for engines with particularly high thrust values.

If you're overvolting it helps to crudely subtract some of the protectors' load before going into the ARC, otherwise it may have trouble winding down, particularly when the gap between overvoltage and the minimum value on the surge protector is very small.

Is it also supposed to trigger itself when autopilot maintain position is on? it makes autopilot a bit funky

No, but you should make sure you do not overvolt more than where the protection kicks in (and fades out). These voltages are configurable through the clamp values and target signals, I believe they should be labeled.

Additionally, you may want to subtract the currently active protection from your load before sending it into the reactor controller, this does not have to be very precise, it's probably ok to pretend the engine power use is linear. Otherwise the reactor will probably only ramp down very slowly particularly when they are close. E.g. overvolting to 1.7 and having the protection at 1.8-1.9

does this have any downsides when overvolting the reactor on purpose?