my tip would be - don't get one
It's emergent technology - expensive - brutally capped with "fines" for going over your limit
a sort of hardware beta version
if there is no other way - you have no option
but if it was 3g or a tincan and string - at the moment I'd take the tin
think how long mobiles were around before "ordinary" people got them.
btw - a dongle is like hoover or biro
one type of dongle is a usb device
but it could be a network, wireless, 3g, gps or any other sticky inny thingy