And why?

I like the small size and light weight of the T-2 but the PRO, being a tad larger in diameter, is a little easier to pick up when throwing the weapon to your shoulder.

I have a PRO in a Scalar Works absolute co-witness mount just sitting in my safe. Bought it last year on Black Friday. My grab-and-go carbine has a T-2 on it, but was thinking about swapping. Yeah, I have too much time on my hands!