Signed up to 3 mobile broadband last April and have had no problems with it.
The reason I switched was that I got rid of the fixed line out of the house as I thought this was robbery.
The performance I am getting from 3 is just as good as I was getting with the fixed line. I don't download films etc, just surf the web, email, buying stuff, booking flights etc, the usual stuff.
Your allowed a 10MB download limit, however for the three bills I have got in so far, I find it a struggle to get up to 2.5MB.
Have used it in Meath, Kildare, Dublin, Longford, Sligo & Leitrim with no problems. The only thing I notice is that down west, you don't get the full bars showing on the reception icon.