this is definitely one of the smarter ways to mix your BTC, even with 0.001 minimum, personally don't see a need to mix less than $3 USD or 20 krone. and with them not taking any fee off the top, relying solely on donations, its definitely one of the better things to put your money towards, if you're trying to mix BTC.
It really is a good way of enhancing your privacy and most of those who use this have a huge amount of Bitcoin and might as well they consider to being generous as a sign of gratitude to the successful mixing of their Bitcoins since they didn't charge you any fee or whatever. Just a donation will help them in return for their services even if it is not that much.