I did have a Vodafone dongle, however did not find it any use on the train journeys that I travelled.
I often did Chester (N.West) to London, as soon as I left the station I would lose signal straight away. However some friends from the south of England do not have any problem with their Vodafone dongle.
My Dad had one like this:
It was useful when our home internet went down, but for journeying it is unnecessary now because so many trains have WiFi and for it's intended purposes it was pretty crap. Pretty, but crap.