Very adjustable. I LOVE mine! Thumb screw lets you adjust it easily while riding. I can lay back or let it push in my lower back while sitting upright. Still has more adjustment left both ways from my usual range.
Check out my other post to see the mod I did to keep it from sliding down while laying back on it.
I have the back rest on my Mustang low down and I like the thumbwheel adjustment. Different jackets have different thickness of back armor which changes the fore/aft positioning, and easily can adjust after getting on. Mine stays in pretty good vertical position but I would be interested in seeing how it could be tightened
I just got back from a 3K roadtrip from Seattle to Yellowstone. I loved having the backrest on the trip.
However, it did slide down on me occasionally. To answer your question, "No, it didn't push me forward and it was nice to have the adjustment on the ride."
I have the Mustang backrest and it works fine. It will slip down but the trick is to set the detent screw just tight enough to keep the bacrest up but loose enough to be able to remove it.
FWIW - When I went to a Mustang Solo with backrest (from the OEM seat) on my 2010 RK, it positioned me down a bit and slightly back. But, as others have said, you can adjust it a bit to your comfy spot.