I've been doing this for years. It's not a substitute for fingerpicking -- the flatpick isn't quite as quick or flexible as a thumb when you're also trying to keep your middle and ring fingers in place to do their part. But it's a fun way to add a little spice to your flatpicking. I have nails on my right hand; don't know how well this would work for people who play with their bare fingers, but it works well with nails.