sight

So I picked up a PS90 today and was wondering what a good optic for it would be. I think a nice red dot should do, but I'm looking for something with a small profile and doesn't take up a bunch of space. This is more of a defensive weapon than a long range one so I won't need anything with...

Should I pay the extra $20 for adjustable brightness or is that stupid and will likely never be used? Seems like the RM02 auto brightness gets raving reviews, and is $20 cheaper. Will be on a G19 carried daily. Help me decide...