I did exactly this when I purchased my 496 last year. From a pilot store. And had a VAT receipt. No problem at all.
It shouldn't matter where you buy it - your local pilot's store could have them on special offer compared to a regular retailer anyway.
As No Foehn says, its a convenient automotive satnav tool which happens to have an aviation mode too. At the risk of starting a holy war though, I have to say that having used both, the Tomtom has a better route calculation strategy than the Garmin does. On the ground, at least!
Paul.