A friend of mine had been with IG for approx 8 years. He closed his account, recently, because he was dissatisfied with the amount of slippage that he was getting. He has moved to another SB Co and I hope that he has a better experience there.
I have only found one SB Co, that I would recommend, without hesitation, and that is GFT. I had an account with them for 2 years, before switching to ECN. In that 2 years, I only had one mini dispute re; slippage and I was trading intra-day with them, every day. On one occasion, their server went down and left me in a trade that I couldn't close. They told me that if the trade made money, they would pay me. If it lost, they would scrub it. That's what you call an ethical company.