AVOID Bulb. I switched to them, and immediately after switching they raised my tariff from lower to higher, without giving any good reason. The hard part is, not ONE energy supplier in the UK seems legit. Some are just worse than others. Avoid Eon, iSupply too. Both are absolute bullies and both overcharge. iSupply are particularly obnoxious.
And remember, it is illegal for them to stop you switching, even if you owe them money. Email the Ombudsman if your energy company are trying it on with you. The more people who complain, the better.