I know somebody who uses meantone tuning regularly on his hammer dulcimer. It makes the dulcimer sound much better, but the problem with it is that YOU CAN'T PLAY WITH GUITARS. The usual result is that the guitarist correctly detects that they're out of tune and then flounders around wildly retuning whichever string they last heard a problem with. Since no guitar tuning can possibly match, this keeps them occupied for rather a long time (no bad thing) but they keep coming back to try playing along with you using their latest failed effort.