The unit works well for a while, but there is apparently a spring in the handle that wears out, or a valve that goes bad, so it won't shut off completely. Unfortunately, the design does not allow those parts to be replaced, so the whole unit must be removed and a new one installed. Mine was still under warranty, so cost was not an issue, but it's not an easy install at all (and I'm definitely not a novice!) 

But if you over-tighten the nut under the sink, the handle won't shut off completely, even on a brand new one. That little fact is well hidden in the :"Trouble-shooting" guide. First, that doesn't make sense. It should be designed so it can be tightened, like any other faucet. But the Installation Instructions should also caution against over-tightening. (Why should it be able to move as I use it?) Seems like a very useful and handy product that needs some serious re-engineering work. Thankfully, the company is easy to deal with, and has no problem sending replacements.