I use a Vodaphone one and its been good where I live. Signal speed can very a lot though when travelling.
Not as good as a wired in line as its slower, signal can drop sometimes, reception varies from place to place. Having said that, I really like mine and like the idea I can use it anywhere I am able to obtain a signal. I find it plenty fast enough for normal info searching – looking stuff up, mail, singletrack etc. I never bother with videos though as it would use up too much of the monthly allowance.
I would say give it a try. Even borrow one from someone who is near where you live now, just so you can see how it works and its possible speed. If you dont like it at all, dont get one when you move.
I think they are good though on the whole.