If you want a quick review... I have a TomTom Rider II, which is widely regarded as one of the two main contenders. It is generally very well sorted and predictable, but the snap on mount is a bit unreliable, and I spent ages checking my wiring before I realised it was the mount that was iffy. A quick twist of the mount before I set off to warn it not to mess me about, and it has been 100% for the 8 months or so.
The bluetooth integration of it to phone and headset has been superb, and it copes well with a seriously obscure dual SIM phone that neither of my cars will use reliably.
Performance as a GPS: 9/10.
Performance as a phone bluetooth device: 9/10
Performance as a bike mounted GPS: 5/ 10
Value for money: 2/10
Overall, good but not perfect, and insanely expensive. The clue is that TomTom were originally a software company, not a hardware one. So, surprise surprise, the software and firmware are better sorted than the hardware.