About three years ago, I bought a MK 72 from a local shop. It had spent a lot of its life in someone's closet, so it was in good condition visually. When I first played it in the shop it seemed muffled, but I liked the design so much that I bought it on the chance that it would open up. It turned out to be a good bet. The MK 72 really came to life after being played for a few weeks. Some of it, of course, was my ear becoming accustomed to the sound of the instrument, but in this case there was something more as well -- the increase in volume and warmth was undeniable. It may be that the more extensive Kasha top bracing needs to to be worked in order to loosen up. I wonder if that was part of the reason these guitars weren't better received when they were first sold.
Over the past three years, I've really had no trouble with it other than some buzzing that was cured by leveling the frets. I had a pickup installed under the bridge and it sounds spectacular through a Roland Chorus amp. The construction quality is excellent (This 72 was made in 1977 in Nashville; so it's one of the later ones). The tone, particularly in the upper registers, is bell-clear with much more sustain than the Martin D18 I've had for 41 years. Based on my limited experience, I'd say these guitars are quite undervalued.