Haz:
They reqlly are two different tools suitable for different jobs. If you are going to be moving dirt for leveling, the box blade will do a lot better job. The ripper teeth will loosen the soil, while the end plates keep the material in the box until you are ready to drop it where you want it. Even without the ripper teeth extended, the box blade will be much heavier and will cut into the soil better than the rear blade.
The biggest advantage the rear blade provides is the ability to angle the blade and side cast the material. This can be very handy for crowning roads and driveways or just moving material to the side. However, since the rear blade is much lighter (unless you add additional weight /forums/images/graemlins/smirk.gif), it will not cut into the soil as deeply or take as much material with it.
The box blade should usually be just a little wider than your rear tires, so that it covers the tracks. Much wider, and you may run out of traction trying to move all the dirt it will hold. A rear blade, however, should probably be at least a foot wider than your tractor, perhaps 2 feet, so that it covers your tracks when angled.
I have both, but I must say that the box blade seems to be more useful for all around use. I use the rear blade only for specialized applications, like plowing snow, where the angle feature allows me to throw the snow to the side as, long as it is not too deep /forums/images/graemlins/tongue.gif.
Keep reading the posts, you will find a wealth of information on the differences. Could be that yoru dealer doesn't sell many because folks buy different brands from those he sells. Good luck with your choice.