I have used a Sears Monster Lawn Vac for about 10 years on my riding mower. The soft top is fraying and I had to replace the big hose but it works OK. The cover on this model did not want to stay closed (as it gets full) so I had to modify it. The hard top units are an improvement, IMO.
My main complaint is unloading it. The bin dumps but the leaves are chopped up and compressed so I still must use a rake of hoe to pull most of the leaves out of the hopper. That leaves me standing in the mulch pile and I need to move the mower a foot (or so) forward a few times to completely empty the hopper.
I thought a bigger bin would cut down on trips to my compost pile but a full load is about all my 22 hp mower wants to pull. Also it gets top-heavy and can tip over if I go over tree roots too fast.
The main advantage of a lawn vac is ease of transporting the mulched leaves to my compost area. The main disadvantage on mine is the manual effort to empty the load. Overall, it is MUCH faster and easier than raking and dragging tarps to the compost heap. It used to take me weeks to do the work which I can now do in a day. I clean up about 2 acres with several very old and large oaks.