I use it regularly, but not as an investment - for me it's a way that I punt on sports such as golf, soccer etc, i dabbled in shares years ago when I were a lad, but I don't know enough about them to bother anymore. IMO it's probably the best way to trade shares (obviously only the bigger ones will be quoted), no commission, no cgt, you gotta keep a very close eye on everything though - i know from experience that spread betting of any sort is very risky!!
I presume that they have some sort of a limited stakes package for beginners that it may be useful to try initially.
Others to consider are Delta and Sportsspread ireland (they have a different name for shares, but I don't recollect it off hand), these are both irish firms.