Dongles
Dont know why you picked the Zoom one when nearly all Dongles available in UK are made by Huawei and ZTE, and when most of those are more or less given away on a data tarriff. Three has its coverage issues sometimes but their deals are pretty good.
BTW, most recent linux distros work very well with 3G Dongles and Huawei at least, work 'out of the box': just plug it in and wait for the config wizard. After that, it's just like selecting any other wireless network