I had a AgriVac unit years ago. While it had the engine mounted on the tongue, it wasn't much different than the PTO driven unit. If you have any number of obstacles to go around or have to back the thing in to dump, it is a royal pain to utilize. Not to mention sticks would frequently plug the hose between the mower deck and the vacuum blower.
I utilized my MCS20 for the first time this fall. It is the cat's meow for leaves. I'd suggest you take a hard look at it.