I'd be tempted to wait until April 1st when T-Mobile are due to launch their "eat as much as you can" data service for 7.50 a month.
I have both a Vodafone seirra aircard 750 and the option globetrotter mobile connect GPRS cards as well as the latest Vodafone Options 3G mobile connect card (courtesy or work)
As others have already said the Vodafone dashboard isn't fantastic but has improved with each release, I believe the lastest is version 6.1 and seems pretty stable.
But most of the time I just end up using a Bluetooth connection to my handset from the laptop using standard DUN, it's much easier and more stable.
Michael