I have just moved to IB from a SB broker and although their trading platform is a bit antiquated, it is refreshing to see the actual market price reflected in the quote, rather than the SB price, which imo is subject to slight bias.
SB prices (for indices, anyway) are based on the underlying futures price, which account for some of the fluctuations in SB prices : ie when the futures start to move, they move faster than the cash price, and this is reflected in the bookies quotes, but not of course in the cash chart of that instrument, which is always a little late.
However, I would not recommend that you jump into using IB without some good knowledge of the industry, as you will most likely get your fingers quite badly burnt. Probably best to learn the ropes using a SB broker for either SB or CFD's.
The tax benefits are clear : there is no tax applied to SB's as they are "a bet", there are taxes applied to CFD's and from futures trading.