They are considered volunteers in the Netherlands as long as the compensation is way below market rates. I don’t understand why you think this is a problem.

In the Netherlands, volunteers can be paid up to €5.60 per hour and up to €2100 per year (tax-free).

You can choose a custom donation and make most of your money go to the EFF. Then the top tier is just like a €24 donation to the EFF and you only really “pay” €10.30 for the actual books.