There are several thousand of these converted guns in use, and they have been in use for a few years.
Over at CAS City, seems like these things are pretty common, so I'll bet they're not something new to the "authorities". In any case, I like BP and intend to shoot mine in BP most of the time. But conversion cylinders are an important part of revolver evolution, so I think it actually adds to the authenticity.
I don't know about people who can't legally buy a firearm using these things.... seems a bit impractical. In my case I want to shoot BP and given the little woman is only going to allow me so many guns, I thought with the conversion, cylinder it may make a "better than a pipe wrench" garage defense tool.