As tipped in MSE, this tariff showed in Energyhelpline comparison for my area, and it is said to normally save you around £200 more than the next cheapest tariff around. What also make this good is the cashback available by Topcashback and Cashback Kings (not available from Quidco I'm afraid) when you switch. Act quick as this tariff should go anytime!
The reason this tariff doesn't show in some comparison website is that this tariff is not available for Economy 7 electricity meters. Untick Economy 7 and it will show on your list.