Looking to buy a sat nav. Any advice on which ones are favourite at the minute for bridge heights/downloads/ best place to buy etc. All advice welcome. 
Probably not the answer your"e looking for but have you considered buying
a decent truckers atlas ?
Am i the only one that still uses a map?
Suedehead:
Am i the only one that still uses a map?
A SatNav IS a map. It’s a map with a few extra bells and whistles.
(And it does from City Street scale to National scale, and it fits in your pocket. No need for a 3 cwt bread crate, brilliant)
Use it the same way as you use a paper map.
ie - This looks like a sensible route from here to there.
Several hours later –
Oh dear, I appear to have choosen a poor route, perhaps I should consider a different road as this one doesn’t seem suitable for this vehicle.
More commonly expressed by " Oh [ZB]". 
a truckers atlas how quaint
Don’t waste your money on a sat nav with all the bells and whistles.
A cheap tomtom used with some common sense is sufficent. I’ve got tomtom 720 and never use most of the features.
Ive got a tom tom 720 and it works fine, managed to download the poi’s onto it, low bridges, truckstops, red fuel depot’s etc. Very easy to use.
over priced and over rated
there are problems with the map data and there are other solution available that are cheeper