I had a long conversation with idealing on this issue and a few others regarding their margin accounts. A big problem with idealing is their financing rates. You pay around 6.5% long and you get 0.5% short if my memory serves me correctly; daylight robbery in my opinion. You also get no interest on margin.
There is always a catch, spread betting firms always have a hidden cost, some requote, other use large or biased spreads; idealing have uncompetitive financing rates! You need to make 6% pa just to stay even, that's ignoring inflation!