I've read about them, but haven't got to try them, yet. I found these...
http://www.zzounds.com/item--AUTAT4041SP?siid=75245&gclid=CML29P-H_cMCFQguaQodrqcAkg I had/really liked pairs of AKG C480b/uls CK61 and SM81's(long gone). I've replaced one of the C480's and then got very interested in the Mojave MA101fet. So, now I have to decide which of those (current) SDC's to get a mate for first. I'm still tempted to get another set of the Shure's. On certain acoustic guitars, they worked great, but I have new/different ones now, and so it's back to the "drawing board".
With this new Warm Audio TB12 and the Hardy 990C+ I plan to put in it, I'll be back to exploring what works best on which guitar(and of that depends on the song/key/flavor, etc). Stereo pairs are a lot of fun!