I've got a couple for my LC9. So far I have used them a few times at the range. They are a little iffy on the first round. I have sometimes needed to tilt it a certain way to feed. I don't think they are at the point where I would trust them for back up mags.
They do provide an awesome grip with the grip extension piece. Like shooting a full size pistol.
I need to run them a little more to gain some confidence with them.