if on stage, i would like to recommend yamaha click station, it has real time volume and various beat control, so it is more practical, like sometime suddenly change songs, so it is easier to set tempo, as u no need to turn the dial to your desire tempo, just key in and save will do.
i did use tama rhythm watch 90, it is good if u only do home practice, coz it has alot of rhythm that u can choose as accompanyment during practice sessions, but when come to real time, diff. set tempo , set volume, and save, all takes longer time.
just try out the rhythm watch and yamaha clikc station, and u will know, which one u prefer.