I have the 5150 and it was expensive but it is a one off purchase. I have let the live updates lapse as I did not like that function anyway. I use my smartphone to look at the destination before setting off and I take note of the map route to see if there is an old reliable road as a lot of times the satnav sticks rigidly to motorways etc. Sometimes the old favourites like A38, A50 and really good arterial routes will get you there much quicker since highways have not shut them off yet every night 
In the end there is no substitute for having a road map of the UK in your head. The times on night driving I saw lorries parked on the side of the road and the driver with a map out trying to figure a way around a road closed by the lovely highways people most of the time I go sailing past and know the alternative but where the satnav is useful is if you know roughly a way around, once you get to the start of that alternative route the satnav will take over and re-plan it accordingly but just watch it is not heading you back to the closed motorway