I too am interested in adding a tach to my R3T. Like you, I've kind of focused on the Dakota Digital. The small (2 1/16") round tach looks great I think. The large (3 3/8") tach is too large for me.
They are programable from 1 to 15 cylinders so they should work without a problem I believe.
The only problem is by the time you add the chrome plated cup and handlebar mounting bracket, you're close to $400 when done!
Round Mini Tachometer
Round Performance Tachometer