I used A1 Visas (umm...probably not their full and legal name, but a Google search of "A1 visa expediters" would turn them up) last November.
I had to call them a couple of times for updates and, judging from others on the forum, I got overcharged at $300. On the other hand, they were very pleasant on the phone and I got my visa within 48 hours. So overall I was pleased.
At that moment in my life, I would have run down the street with a basketful of money throwing it at people to get my visa in hand...