I have a pair of them. I like them. I've used them for drum overheads and on acoustic guitars, and on some percussion.
I've heard people say that you should be able to use small diaphragm mics for vocals in a pinch - I tried
the Pro37Rs for this and they weren't really that great for it, I thought. In my experience, the upper mids and highs are more present with them than lower frequencies - voices sounded thin.
However, I think they work great paired with a large diaphragm on acoustic, or with kick and snare mics that get a little bleed.
That said, I should also add that I used a large diaphragm condenser paired with a Pro37R on an acoustic guitar track for a tune I did with a lot of instrument tracks - in the final mix, I ended up using only the Pro37R track alone, rather than paired with the LD condenser. The Pro37R track sat in the mix better and gave me a really great and useful sound for that tune (it's on my IUMA site, called Run Dog Run if you want to check it out). The guitar is a 74 Martin D-35.
I think, at the moment, that the big 2-fer sale of Oktava MC012s at Guitar Satan is probably a better buy. But I haven't swapped my Pro37Rs out yet. When I do, I'll step up to something much nicer, like the Josephsons.