The Meyer Sound HD-1's are a set of high definition, active studio monitors. They are sold as individual speakers I believe, and are pretty much suitable for whatever sort of use you'd like to use them for. Having said this, they're probably best suited as near field monitors for monitoring and mixing. The HD-1's would also be suitable for mastering and other audio applications. You've got room control in the back and all that, and they don't require any sort of power amplifier since they are active and already have one built in.
The Meyer Sound HD-1's clearly have an impressive sound, as they're loud and quite bright sounding. They also do have a very nice amount of low end, especially impressive since there isn't any subwoofer. However, in general they're definitely pretty bright sounding, with a very crisp high end response. I've used these monitors for monitoring during tracking, but they can definitely be used for any sort of use inside the studio. These sound like they would be perfect for mixing because of their super detailed sound, but I've yet to try them for this application.
The Meyer Sound HD-1's definitely belong in a professional studio, as they have a big studio type of sound for sure. I don't think that they would be my first choice for a set of all purpose monitors if I were putting together a professional studio since they're a bit bright sounding for me, but they should definitely be in the discussion. Of course they're going to cost you a good amount of money, although I'm not really sure how much we're talking exactly. If you're looking into a set of high end studio monitors for your professional recording studio, I'd encourage you to shoot out the HD-1's along with some of the other high end monitors out there...