By far the main issue for me with capos is tuning stability before the audience. I've tried many (Dunlop, Shubb, G7th, Daddario) and none works. They all randomly detune the guitar, sometimes 1 or 2 strings, sometimes only the low strings, etc.
Even if you put them on the fret, which is the best position in that regard although you lose some sound resonance.
I dream of a reliable capo.