CFD trading is legal and highly regulated in the UK, as is its variation, spreadbetting. Both have low deposit requirements, very small minimum position sizes, SB has no tax implications. In terms of TA/FA, neither is any different from each other or from trading using any type of forex broker. Markets offered include large/medium cap stocks, indices, commodities, forex, bonds, /ETF's & sometimes "specials" like interest rates.
Winning clients are a very low percentage, as these platforms are available to the least capitalised, least prepared newbie, so its more a reflection of the low standards of the clients than any inherent difficulties in CFD or SB trading.
If they're accessible to you as a client at all, they're probably best used as a beginner's introduction to trading.