Have you released both sets of bellows? There are two sets of bellows, one on the reed side and the set you pump. Both are held by a catch and you need to release both to ensure a steady flow of air.

Suibhne, the M1 shruti box is made in the UK and the standard of construction is pretty good. That said, I found I had to adjust some of the screws holding the "keys" to ensure they moved easily, but were not too loose.