The two bar style I heard once it's set up, you just slide it back in or out and the cross hair will be leveled. The clamp on you would need to check and adjust that the cross hair is line up straight every time you take it on and off. As for images quality this is just my opinion since I don't have one to test. But seem clamp on would be better quality since it slides over the back or the scope and no light will get in. Only light gets in is from the front of scope. With the 2 bar style, the mount just butt up against the back of the scope and my concern if light will leak from the gap creating halo effect or something, effecting image quality. But this is just a theory, idk. Also another theory is the clamp on sit behind the end of the scope, it would add weight and shift the scope down causing poi shift? Idk.