I own both, I use the volo's with my wetsuit and the quatro's with my dry suit. I find the volo's really shine on a surface swim, the hinged blade seems too allow a better stroke without the blade popping up out of the water. The volo's definately cause a lot less wear and tear on the leg muscles and I've never really noticed any performace issues in currents (but we usually don't have much current here). The quatro's are nice solid blade fin that's going to perform as reliably as any other fin.
As far as the hinge breaking, this was supposedly a problem with the first production of the volo's but was fixed on subsequent productions, if the volo's have non-locking abs buckles, they are first run and don't buy them.
I can't say which I prefer, I like both.
Steve