I think it's more a marketing ploy than an especially useful item.
IMO I don't think they are all that great an idea. Maybe for mounting a laser, but crimson trace makes grips that serve the same purpose. Mount a light on it and you have to point the gun at what you want to look at, not a good idea if it turns out to be your kid or wife, etc..
I don't know of any concealment holster that would allow using the rail. There are thigh holsters and some really flimsy looking ones. But nothing for concealed carry.