I've now replaced my hardwired Bury cradles for the Kaiser with the Bluetooth versions (and TyTn charging leads - extra) and they seem to work fine.
The phone works hands free, charges, mutes the radio when it should and leaves TomTom talking to me through the internal Kaiser speaker. Tom Tom only mutes during a call. Voice quality is fine for my use.
The cradle can be used with various bluetooth phones and, rather than being made to measure for a particular phone, it is adjustable to fit pretty well any type. One slight resulting nuisance is that I occasionally switch on the camera as I insert the phone (the camera button is on the side where one of the clamps is). Easily sorted by pressing the red key on the phone however.
So I'm a happy punter again. Thanks to phonejunkie for sorting me out.