That Tillman looks exactly like my Bri-mar!! Dump trailers are the best things ever. All landscapers should have one.
Nothing to add that others have not said. Get 12' long at least, stay away from the weak single cylinder lifts, stick with dual or scissor lift.... something low profile (easy to work out of)... get built-in ramps
And make sure you can haul it and STOP it! If getting one over 10,000 lbs GVWR, watch that you're not towing it with anything that in combo pushes you over 26,000 GCWR... that's CDL territory- I had to get one with my 19,000 lb F550 and a 12,000 GVWR Bri-mar.... if I had got an even 10,000 lb trailer, I'd have been fine, but I don't regret it at all.