I use these as accordion microphones to great effect. they were a bit pricey (not as much as some of my tune mics though), but I definitely got what I paid for, plus some more! I love these and have used them on all sorts of applications.
Short on cash I couldn't spring for the Neumann equivalent, but these guys are more than adequate.
Sometimes I add my TLM 103 in the middle if I'm doing something like a guitar.
I initially tired this to compare the quality in sound, and turns out it's a neat trick for beefy acoustic guitars!
As far as quality goes, for the money they're outstanding. They are a little nasal in the mids somewhere, but not noticeable till comparing the sound to another superior mic.
Also, they are obviously hyper directional so ideal for countless other 'mono' applications..