Ok. After my post saying I use a UTG riser mount and it is good, I will tell you that almost anything else except a few UTg items are crap. I wouldn't trust anything electronic of theirs.
Riser height will affect how high that sight sits on your receiver, and how much of your front sight is visible as you look though the dot sight. Absolute cowitness would put your front sight right in the middle if the window pretty much. Lower 1/3 co witness would put the dot sight up higher so that the front sight would only be visible in the lower 1/3 of the window. Not having a riser would likely put the front sight base in the entire window of the dot sight. None are a really big deal, with a dot sight and keeping both eyes open one eye will
Look at the dot and the other should look at the target and your brain puts the dot on the target. Some folks still find that more than 1/3 of the window having the front sight in it is too distracting so they prefer a lower 1/3 cowitness. Other folks like absolute cowitness, because it is kind of like looking through a ghost ring or aperture rear sight.
It really comes down to personal preference and what is mist comfortable.
I also have used the TRS25 from Bushnell, on an AR for over a year, and one season on a .30-30, as a bit if an experiment. It's still doing fine.