With a clip on you are zooming in on the screen generally. My pulsar works fine 3-10 x for example but it has resolution on the screen pixel. I gernally feel comfortable setting the zoom to 6 for example and hunt.
I learned pretty quick that a quality clip on is going to be big $$$$$ for something that has a reliable return to zero. I got an agm rattler tc19-256 but soon realized attaching directly to the scope would not be reliable. To solve for this I started attaching the thermal directly to the rail. I got that worked out but I ended up getting the eye piece for the thermal also so I could use it as a spotter or stand alone scope. The rifle ended up being a little heavy for me with scope and thermal so now I usually just go with either the scope or the thermal depending on what I'm doing but if I'm sitting in the blind and not moving I can use the thermal as a spotter then clip it in front of the scope pretty quickly.
Any concerns on AR type guns with the forend/handguard rail flexing relative to the upper receiver's rail? It's pretty easy to push most handguards around a little bit. And with the clip-on mounted to the handguard portion of the rail, it's relationship to the upper receiver mounted scope is not "fixed".
It seems to me that you'd want to use a gun with a monolithic upper like an LMT.