To make it short, if you play alone on the accordion, it may help you to get sound out of an amp or PA, but if you play together with more people, your sound is gonna drown. The mics are somewhat ok, but you can see it on the construction, how on earth are these short arms going to pick up sound from both the treble and bass?
Buy instead two Akg C516ml, and place one on each side of the accordion.