I agree, IMO all the 'fake' cakes aren't worth it. Just have proper cake and syn it! However there are loads of recipes out there for cake made with weetabix or scan bran, just google 'slimming world cake' or look at 'scan bran recipes' on Facebook.
There is an apple sponge on the SW website that isn't too bad but it really is the best of a bad lot - it is just an ordinary fat free sponge using proper sugar with apples and cinamon in and is about 5 syns for a decent sized piece.
I wouldn't have anything with artificial sweeteners in but plenty at my group rave about them.