Midnyte has a definite talent for writing the Invincible cast, which is very much demonstrated here. The characters are written like their show counterparts (albeit if Mark & Allen were bi & secretly sluts), complete with Allen's "Bro" energy & Mark giving people really weak excuses to cover what he's really doing.
We're not shown exactly when the two of them started doing it, which could make an interesting prequel if Midnyte ever cares to do so; but here this is an established thing, which allows us to skip the setup & get right to the action.
The sex is well drawn, with a nice mix of positions & you can very much see how much fun they're having, as well as why a certain someone just can't resist staying to watch the show (and in fairness, I completely understand that). The art conveys the mood beautifully, our boys aren't making love, there are FUCKING.
Definitely recommend this one & its sequel.