Does the organisation you’re giving to allow you to set up a regular direct debit with Gift Aid? I’m pretty sure EA Funds does this, so anything you can donate to through there would be as easy administratively as doing the GAYE scheme, and I don’t think there’s any fee.
The real benefit from the GAYE scheme would come once you’re looking at claiming back tax for yourself (i.e. when you start paying more than Basic Rate tax). And even at this point there are other options. When I was giving fixed amounts on a monthly basis a few years ago, I used the live chat on HMRC’s Income Tax Page to notify HMRC about my regular donations, and they updated my tax code to take them into account. (my employer didn’t support Payroll Giving, otherwise I might have done that instead)
Thank you for writing up your notes and thoughts on this book! I hadn’t heard of it before, and have since read it. A lot to think about and research—I’d be interested in sharing notes and may write some posts looking into specific claims he made in the book.