Any idea how good these are?

The only thing that's likely to change actual stopping distance is the pad compound. The other parts may alter pedal feel but not stopping distance. It may be a decent compound they're using (it's certainly not hard to top the organic compounds in many parts store brakes), but their website doesn't feel like a serious high performance brake company's website, either.

What do I mean by that? Well, take a look at Carbotech, Hawk Performance, or EBC. You'll see a choice of pad compounds for different types of applications, photos of race cars running their products, directions for how to break in their brake pads, stuff like that. All indications that these guys put their pads through serious testing, know that not all types of pads are appropriate for all drivers, and in general are serious about performance.

If I wanted to upgrade my drums without going to discs, I'd probably either get Carbotech to reline a set of factory brake shoes, or go with the carbon metallic shoes offered by Firm Feel.