I have not used an m88. But I had an M69 for several years and liked it very much for tenor sax. It was something of a "go to" for me in that application. That being said, if the saxophonist likes to move around a lot then I'd switch to another mic. As has been mentioned, it has strong rejection and the sweet spot is relatively narrow.

The M69 also seemed to do well with vocals (excelled on some female vocals) and guitar cab.

I sold the mic a few years ago when I needed some $. That was NOT a smart move. I didn't get much for it and quickly found myself missing it.

So I ended up buying another.