Lets face it nothing will be as good as the original FITs !
So its a pointless exercise trying to compare with it, maybe compare it to the less than 1% in a cash ISA or the NS&I Green Savings bonds of 1.3% which are evaporating your lump sum with inflation.
The main advantage which you wont get anywhere else, is it goes a long way to fix your energy bills for the next 25 years or more. Energy bills go up, your savings go up, energy bills go down your savings go down. And for most people the returns are tax free.