Very worthwhile... a godsend in the Lake District with all the hills. Expensive though, mine was £3100
But you need to pick the one that is correct for you... if you're an experienced cyclist and just want a bit of assistance to help you extend your rides, then get a road/racing bike which will have a smaller motor, but will allow you to use the bike motor-less without much additional weight.
If you just want to get around as easily as possible then i'd recommend getting a touring/hybrid bike with a bigger motor, but these tend to be a lot heavier and really you need to use the motor all the time. (this is the option i took, as it came with in-built lights, mudguards, luggage attachments etc)