I use it. It's pretty neat (gauge 12 with nice black rubber that is not too thick). I don't think they have the certification for in-wall (otherwise they would advertise it). You might want to drop them an email; they are always eager to answer questions.

I know that monoprice.com and Bluejeans have 12 that are certified for in-wall application and that are not expensive at all.

See Mojo's signature