It does seem expensive, but it just isn't a mount, its basically an addition to your Tomtom and makes it work how it should. I looked into it a lot before i bought the Tomtom App for my 3GS and all the videos on Youtube showed how much better reception you got, along with everything else when you had your iPhone in the mount.
I think I bought the app one night and went to my local apple store the next to get the mount before I went to Manchester and it worked a dream.
I've never had any loss of GPS with iphone 4 and the tomtom mount either i don't think.
Oh, and it also doubles up as a handsfree thing too, you can answer incoming calls from it, etc etc. and their voice comes out of the built-in mount speaker. :thumbup: