Whats the difference between this one and the one that you have listed for $119.97?
This one has a glass etched reticle, the less expensive version has a wire reticle.
Is this suitable for a Benjamin Trail NP2?
Yes. Good choice.
what's the highest quality mount/adapter to install this scope on a RWS 54 Air King air rifle? Will this scope endure the double recoil?
You will need a UTG Drooper Mount #PY-A-2297 . It compensates for barrel droop in which these rifles are known for. Yes this scope should hold up fine. The drooper rail will keep it from moving.
Will this scope hold up to the beating that a Diana RWS model 54 is notorious for? What are your recommendations?
This scope should work just fine. UTGs are built strong.