What is Vibrato and what is Tremolo out of these three examples I am not even going there.
Tremolo normally means modulating the volume (without significantly modulating the pitch). It makes it sound like you're trembling because the sound comes and goes very quickly.
Vibrato normally means modulating the pitch (without significantly modulating the volume).
The point is that the only way to modulate the pitch on the concertina is to modulate the pressure (because reeds play flat when the pressure increase, which is why concertinas always sound out of tune!) - but then you'll get far more of the tremolo than the vibrato anyway. So, in practice, I don't think you can't do vibrato on a concertina, just various forms of tremolo.
The vibrato on fiddle, cello, voice(?), pipes, whistles etc is/can be, well, vibrato, because it works on the pitch, not affecting the volume much (though most can do tremolo too). I think this is the case for wind instruments, but maybe I need to be corrected.
So, avoiding any terminology controversy, the wobbling you can do on the concertina is completely different from the wobbling that is done on most other instruments.
Generally (in my experience) vibrato is used on other instruments to make the sound more interesting/expressive/"musical". Temolo is normally used to add tension - probably because it's the same effect you get when you're nervous/afraid.
The tremolo on accordeons with multiple reeds per note works by the two reeds being slightly out of tune, so as they come into and out of phase the sound gets louder and softer.