I've thought about getting one of these as like you said, a little deterrent. Of course like was mentioned if someone really wants your bike and are determined enough, they will get it. But, I also believe in the 99% of thieving assholes out there are just looking for a quick and easy job and would at least give your bike a second thought, which might be all you need.
I don't have a garage, so at night in my apartment complex I lock the handlebars and have two Bully brand brake locks, one for front and rear. Then I cover the bike. I know it sounds like a pain to do each night, but it makes me feel better, and that in itself is worth the money.
I think one of these grip locks would be a good idea to carry around with you running errands around town or what not, just to have as a simple deterrent.
Slow is smooth, smooth is fast.