I've guided all summer using this instead of my Gri-Gri for belaying seconds. The key characteristic this device offers is it's lack of friction while taking in slack. On exposed belays if you are being belayed by this device off of an anchor you can weight it while tying into the anchor with out the worry of that little rope "creepage" a Gri-Gri may have before locking. If lowering directly off the anchor I highly suggest redirecting your brake hand for better control. The added friction in a top-rope system seems to allow for smoother lowering. Rappelling is awkward and not recommended (how often do you rappell single-strand anyways?) One interesting characteristic of the Cinch is that you may install it on a loaded rope. This may have some handy self-rescue applications that I have not fully explored yet. Also, the Cinch has less moving parts, and no spring mechanism, so it may stay cleaner longer. It also might wear ropes quicker than a Gri-Gri, especially if used for rappelling single strand. Some comparisions with the Gri-Gri:

Cinch Gri-Gri Difference
Price 59.95 76.95 17.00
Weight 150gr 225gr 75gr
Min Rope 9.4mm 9.7mm .3mm

Bottom Line: If you already own a Gri-Gri you might want to invest that $60 somewhere else, like a handy set of hexes, unless you pull a lot of shoulder working fat rope up many pitches of slab in a work day. If you are contemplating Gri-Gri/Cinch I might lean towards the Gri-Gri since it is a little more "user-friendly" due to it's spring loaded camming.