I know a guy who used a DeWalt rotating laser level and a home made attachment for his bull dozer blade, used it to make a riding arena surface.  Basically he used the audible tone from the laser sensor to manually adjust the blade-- no fancy (and expensive) valving and controls.  Came out pretty well too. 
The expensive automated things let you use lower cost labor and get the job done faster-- so it depends on what you want to do.  For a one shot personal use project, I'd use a home made gadget, and the rotating laser can be used for other things besides flattening surfaces.  For commercial, the thing would probably pay for itself with one 50K ft**2 warehouse just in concrete savings if it works as good as the mfg claims....