I agree with DonMeixner about the 21 chord 'harps. The higher strings are unplyable if you play the flat against the chest method. I have two "semi-diatonic" A model Appalachian 'harps that I've modified to 10 bar harps with the chord bar hoders moved close to the string anchor end of the 'harp, giving me lots of room to play the short strings. One is D/G. The other is an A with a G string so I can play the A7 chord. I have other 'harps, but these two satisfy my needs. If I need a key or chord that's not available I'll play guitar, banjo or mandolin.
Bryan Bowers uses diatonic 'harps and will often come on stage with a stack of 5 or 6 'harps.