The action certainly isn't stiff. I've had some trouble getting three keys to sound together when I want them to - which is probably down to finger positioning more than anything - and I was probably compensating by mashing the keys down hard. It may also be a weight-bearing problem - I've had difficulty striking a balance between hanging-off-thumbs (uncomfortable), propped-on-little-fingers (very uncomfortable) and sitting-on-knee (comfortable but no control), and I think I've been unconsciously compensating for that by bracing the concertina with the key-pressing fingers. I'll try again later & see how it feels if I make an effort to press the keys lightly.