I recently purchased the Navigation controller to play Resident Evil 5, I have not tried the controller with any other game so my review is soley based on the experience from that, and it is a very pleasant one.
The controller does everything you need, it fits in your hand nicely and all the buttons are easy to reach and use. It has two buttons on the back L1 and a trigger for L2. It also has the full d-pad and the x and o button. All the buttons are easy to use during gameplay and feel very natural.
The controller fits into the docking station much like the other move controllers, but seems to use alot less battery life as I have only charged it fully once.
It made the whole experience of playing Resident Evil alot better and for 17 pound it is a very good price. Although the controller is very small and may seem expensive it changes the gaming experience and will definately be used again on games such as Killzone 3 and Virtua Tennis 4. If you have a Playstation Move then this is essential.