the 5% margin can give you hugh exposure, assuming there is the liquidity. A £10,000 investment on a CFD can give you the equivalent of £200,000 in the particular stock on indices. Some CFD firms have minimum amounts you can use often £5-10k.
IG Markets would not let me open an account with £5k, they said I had to have a minmum of £10k.
Also you have to pay commission on CFD's on a £10,000 stake/bet/investment at a 5% margin you would pay 0.25%, which would be £500, plus you have to pay interest on that £200,000 as well which can work out quite a lot.
Finally on CFD's you need to be classed as an intermediate investor, which kind of waves some of your rights when it comes to complaining about losing lots of money down to bad advice or something.
All of the above may be rubbish, just what Im told. But I think with CFD's you can get a much larger exposure to the market than spreadbetting.