Yeah it looks like it would cost more than a conventional rear dumper, and is a specialized piece of equipment for some rare occasion that you can't back up to where you need to dump your load, a difference of 5 ft.
One application it would come in handy for is back filling behind a newly installed curb with top soil, dumping a little at a time as went along. Also back filling a utility trench in the road, if you could drive along and meter out the fill (sand or gravel) as you go.
But for the average weekend warrior who would benefit from owning a dumper, I really don't see any advantage, and really you'd be limited to just dumping fill, none of the other things we do with these small conventional dumps, like loading logs, moving equipment etc. etc.
JB.