I bought a cheap 60 quid Jimwey 7". It worked fine for a couple of days then, luckily while I was unloading, dropped the satellites for 30 minutes. Next day the screen started to black out for about 30 seconds at a time. Not good in Central London. I lost confidence in it and bought a tomtom 6000 from a TN member (Thanks). Not let me down so far.
Well, mebbe once, when it sent me down a little back alley with a right angle turn at the bottom. That was a bit hairy.
Cheap is not always reliable.