canoetrpr,
I've had both the hinged and fixed rear blade versions and they're very different to use. In general, the hinged are very aggressive in both directions because the other blade is always out of the way. But sometimes you just want to "smear" rather than "cut" and a rigid rear blade lets the two blades interfere with each other enough to do that. Also, you can get the rear blade elevated enough so you can "backdrag" with the front blade going backwards. If that's what you want to do, maybe you could bungee the rear blade completely up without having to hold it rigidly in some intermediate position. I think a rigid rear blade combined with a hydraulic top and tilt might have some advantages over a hinged rear blade. It still wouldn't address one problem we have in S. Indiana- red clay. It seems to pack in the dead space between the two fixed blades and its **** to remove with all those bolts in there.
John