With CFD funds the deposit/margin is mixed with the companies account so if they become insolvent you are only treated as a creditor. With spreadbetting you are covered under the UK investors compensation scheme up to a limit, as with conventional sharedealing. So in practice spreadbetting it is less risky than CFDs if it were not for the spreads and bias.
I understand the betting tax which was originally paid by the punter is now levied on company profits, however they will wish to pass this on of course, hence it is still paid indirectly by the punter.
Except for this there is little to choose between a rolling spread bet like deal4free offer and a commission free CFD like idealing offer except the terminology. I am not sure if this is what defines the difference.
Of course trading and investing are games of chance under a different name, the only thing that matters is the quality of research and how you handle your money. Certainly the tax treatment of these products is a potential hornets nest especially if Mr IR tries to get two bites of the profits.