I would pass on this. Here is why...
1.) Grass will pack by the end of the day. I know this because I bag everything. I have a truckcraft insert with straight sides and a flat floor and sometimes have trouble with the load sticking in the bed if its damp or wet grass. Imagine what will happen if you have a floor that is angled like that one is.
2.)Same point with leaves, except that with a regular style dump insert you have a tailgate that can support a leaf loader, whereas with this unit you can't do that.
3.) a 3500lb payload is nothing when you are talking a load of dirt or stone! You may not think you need it for anything other than mulch, leaves, or grass clippings now, but think of where your business could possibly be expanding in the next few years?
The biggest problem I see with this unit is the angled floor at the back of it. It really limits your loading/unloading potential. You won't be able to load a pallet of material because of the angle. It will make unloading wet/damp/packed material a pain, no tailgate to work off of. It shows that its removable, but honestly... are you going to build a contraption like they have just to store this thing on??? plus have the room to store that?
I didn't see how much these go for, but you can pick up a used QUALITY insert for under 2k. Just my opinion, hope it helps with your decision.