For anyone with the TomTom Rider V2, this is an excellent accessory to have. Given the higher cost of the TomTom Rider compared to a dedicated car unit, rather than buy a second satnag for the car, use your bike satnag.
The Rider unit on it's own is a substantial piece of equipment and with it fitted to the in-car adaptor it's a bulky piece of kit - no way could it be as slimline as a dedicated car unit. In spite of it's bulk and weight with the Rider attached, the attachment has no problem holding the whole assembly to a car windscreen. Viewed from the driver's seat, the Rider in it's in-car mount is no more intrusive to vision than a normal car unit.
I've seen comment that it's too quiet, but with the Rider volume up at 100% it's certainly more than loud enough.
Thumbs up for it from me.