Well, that soon escalated from £20 a side!
I suppose £350 for discs, pads and new calipers isn't too bad, the calipers are not the cheapest from ECP.
The handbrake is not fantastic on the Jazz at the best of times, and as springwood says, the new friction and discs will need to bed in. The handbrake obviously needs adjusting up, I would expect that in with the job, so press for it FOC.