The studio I work for owns one of these mics, so I use it fairly often. This is a ribbon microphone, and like all ribbon mics, it can only be used in the studio. These are among the most fragile mics ever made, so keep that in mind when using it. It uses a magnetic ribbon that physically converts sound into energy using pretty old methods. Therefore it has an almost "vintage"-style sound to it. I gave the mic a little less than perfect rating in this category because of how fragile it is.
This mic has a fantastically warm sound to it. Ribbon mics are not as good as condensers are at picking up the higher frequencies, and will pretty much roll off certain ones. However, this can be great for picking up certain sounds, which don't always require such brilliant high end. Vintage style recordings were great for this reason, so it stands to reason that these mics will work great at getting sounds that are warmer and smoother than shrill condenser mics.
I've used it as an overhead mic on drums, and I think it was this use that was my favorite. It gave me a great, mono-style drum sound similar to the old Beatles and Beach Boys recordings. It picked up all the instruments on the drum kit including cymbals, toms and snare with great tone. I also liked using it on a electric guitar I had that was incredibly bright, after micing it with this mic I managed to take some of the shrillness out of it, leaving a smoother, fuzzier sound that I really enjoyed. This will work great on acoustic guitars for the same reason. I also like using a pair of these to record strings, as they give a fantastic richness to the instruments that reminds me of Motown and other older recordings that feature orchestras and strings.
This mic is really pricy, but it's worth it if you own a studio and want to increase your sonic pallette. There are no mics that sound quite like ribbons.