Elmores has one and I've seen it in action. I watched them load about 50 mags in a matter of a couple of minutes. They work and the rounds stay in place until shoved into the mag. Cool set up and saves a lot of thumb wear.
When people tell me they gun I don't ask them to prove it by letting me see them shoot. I ask them to fill a mag.
A bit easier to toss in the range bag, and cheaper.