I think they are the wave of the future and make the most sense, 699 a side is good. On a Hustler HD it will cost you 15 to 16 hundred for motor and pump for a true heavier commercial unit so it is gives and takes.
If you are loading the system hard constantly I would think a Hustler HD style drive would be the way to go other than that for your average Joe a 5400 approach of just run'em use them up and replace at a lower cost.
The Hustler style drives allows you to handle more weight if need be, you could pull tow behinds with a Hustler system setup right and a current style all in one unit would not be up to that.
They can make the all in one bigger and Better, also more oil capacity and a oil cooler is always welcome if you are running real hard.