Have tried girlfriends tomtom several times on a route where I doubted I was doing the shortest route. In most cases it took me considerably longer. They are fine if you are hopelessly lost, apart from that they are Krrapppp
Will get a satnav myself when I know what a good one is. Guess that once you know the ones that don't work, any of the others will be a good choice
Get yourself to Aldi Ben, had a Medion from there a few years ago, very good until some scrote had it away. shortest and fastest settings in menu. very good and cheapo.
Map book for £1.99 is the best direction finder in my car