Based on a comment from @chrismccannIRL, I decided to take a closer look at the impact my Eddi has had on my grid imports. In this video I will compare its performance against last year. They aren't cheap to install, so if you're thinking of one, the figures I run through here might help with your decision.
Whilst my Eddi isn't going to pay for itself anytime soon, the reduction in gas and grid electricity is worth the cost to me from a CO2 standpoint.
If you have a solar diverter installed, I'd love to know how yours stacks up against mine. Let me know in the comments below.