|>>|| No. 24899
Problem is it eats through your data. Heaven forbid you want to use it abroad. As for actual satnavs, any old one will do. My Garmin cost £70 about 3 years ago, it was the cheapest one in the Currys I went past when I was lost in Birmingham, and it still does me fine today. Most worthwhile impulse buy I've ever made.
Really though, it's 2015, they're one of those gadgets that if you manage to buy a bad one of, it's because you're a moron who bought a Chinese knock off on eBay for £30 or something. Smartphones have made them pretty much redundant in the same way as standalone MP3 players and cameras, so there's a pretty uniform level of functionality across the board.
Your most serious purchasing decision should probably be whether you prefer the interface on a Gartmin or a TomTom. You can pay extra for gimmicks like live traffic information and whatnot, and I think most of them already have stuff like speed camera warnings built in as standard by now. I can't actually think of a single feature I really desire in a satnav beyond telling me where the fuck to go, though, so if you're anything like me the basic model should be fine.