I actually got round to looking at the Moonriders web site. I was a tad surprised to note it said that up to 75% of the amount raised by a rider would go to the nominated charities, and at least £100 must be paid across by 1st April. Elsewhere it says that no more than 30% of the fund raising target would be paid by your nominated charity to cover the rest of the entrance fee (on top of the £59 deposit the rider pays).
In other words, if I were doing a charity ride, and raised say £1,000 for my favourite charity, but then they'd get gift aid on top. It implies the organisers could be getting a maximum of £300 out of a potential £1,000 raised, leaving the charity with £700 plus a bit of gift aid.
They've got a range of major charities listed.
I'd be a bit concerned about all that. It's all very vague.