I've never found them to be stiff, usually quite soft and supple straight out the box. They do, however, start to mould to your wrist and create a gentle curve. I can see how the buckle is slightly annoying though - sturdy and secure doesn't naturally translate to comfort I guess.
I hope it's not a bad (stiff) batch but you could always try rolling it up and leave it tied in an elastic band overnight to see if it helps.