I have just gone through the same dillema - MFD2 or TT300 - in the end went for the TT300 - ?369 inc speed camera database preloaded, plus 'free' usb memory card reader, delivered -
www.satnavsystems.co.uk. I really couldnt justify ?750 for the MFD2, much as I would have liked to.
It also has bluetooth to link to your mobile if you want it to; so not sure what extra the TT500 gives you ??
Fits very nicely to the windscreen using the suction cup holder thingy, and does not look at all out of place.
I've only used it for 2 (local) journeys so far as my wife snaffled it off my the day after delivery for a trip up North ; but the observations I've made so far are that its OK, but not brilliant.
The map data does not seem quite right - I have found two places where it claims the road layout is different to what it actually is (IE. it sees a road that has no junctions as having a juntion in it directs you down !!; and a double mini roundabout that it sees as a normal non-roundabout junction)
Also, although you can do postcode entry, it only observes the first half of the post code and you have to know the street name and number. EG. the postcode GU14 9EZ specifies a street and a handull of houses within the street. The TT will only observe GU14 9, and then you have to tell it the street and number. Whilst this does not sound like a big issue, its a right pain ! Very often you only have the postcode and not the street. TT insists you give it all the info, so if you dont know the street or number, you either have to guess or you are stuck !!
Other than that, it seems a top bit of kit though.