Yes, I tried it a couple of years back and I can honestly say I didn't notice any difference in the veg garden.
It could have made a bit of a difference in the polytunnel though, but it was a bit marginal and could have been the result of any number of reasons.
I certainly didn't get any huge veggies that they put on the web site and I don't think I will get any more.
Tony
Disclaimer: I almost certainly haven't a clue what I'm talking about.