I have used those mobile broadband dongles from a couple of different networks. I have DSL broadband at home and there is no comparison. Don't get me wrong the mobile one is ok for emails and light surfing but if you want to really use broadband stick with DSL. Just my thoughts.
I also have vodafone home phone & internet & find them very good. Reception in my area (by neighbours) for mobile is very slow and I live in central Dublin!, so like selfbuilder I woudn't change either . If costs is a motivation why not check out callcosts.ie and see what your options are?