Not a dumb question at all, but it is one that has been discussed on other forums - so have a good sift thru'. The bottom line appears to be that you pay your tax via the wide spread of SB or enjoy the narrow spread of CFD's and pay tax in the conventional way. However, beware that some CFD providers offer 'free' trading (e.g. D4F) but their commission is hidden in the spread. Personally, I can't see the point in doing this - you may as well take the tax advantage offered by SB. If I ever open a CFD account, it will be one that mirrors the underlying instrument. Horses for courses really. Lastly, if you're new to trading, most people would advise that you start with SB and move up to CFD's - which is a more sophisticated trading vehicle.