If You Can Afford it, Get Two!
The world of ribbons scared me a little bit before I entered it--stories of deadly phantom power, damaging wind blasts, etc. However, I purchased a matched pair of R-101s and have never looked back. Guitar cabs, acoustic guitar, cello, violin, mandolin, percussion, piano, drum overheads, drum room, and more (I'm sure) all sound fantastic through these mics.
One single R-101 is great, but if you can afford a matched pair, don't hesitate to make the purchase. Keep in mind these mics perform best when going through a ribbon preamp. I currently use The Ribbon Pre by AEA with the R-101s, and I couldn't be happier with the sounds I'm getting.