I clamped mine directly. Looking naturally thru the center of the optic, the dot is comfortably above the front sight. Gotta say too, I've not spent much time with red dot sights, but on this PCC it works incredibly well.
Yes it is. I bought it long ago, 2nd hand. Never really had a use for it til this PC Carbine came along. In spite of the miniscule price, and probable mediocrity compared to higher price units, I am pleased with it.
I doubt you'll need a riser for your application. The TRS25 is a pretty good sight. If I were putting a dot on a SD carbine, I'd spend a little extra and get one with the 'shake awake' feature. The AR9 PDW hanging above my bed is equipped with a shake awake dot.