I used Njalla. It worked fine for me and was really simple to manage. In the end I decided to switch since their strength is also their weakness. You don't own the domain, they own it. They register it to their name and you can manage it but when they go bankrupt (doesn't look like it) or decide you are violating their terms (and maybe you aren't but they still decide that you are) they can cancel your service and you are not able to get your domain back, since it was never in your name.

There are stories from people who lost their domain. But I only heard about this from others and I always find it questionable about why these people are coming out with these kind of stories, were they really not violating the terms or were they and are just upset that they got caught...

Njalla works this way to make sure nobody knows who you are and who registered the domain, because even if law enforcement would ask for the owner at the tld registrar they would get Njalla as the owner. And you don't need to let Njalla know who you are, so that's where it ends. But in the end I got nervous that someday they would cancel my domains or that they decided to stop the service and I would lose access to my domains and email. Is that a legit fear? Probably not. I have had domains with them for 5 years and never had a problem. You can transfer your domain since you can request the transfer key via the admin page and you will recieve one instantly. So you don't really notice not owning the domain until something happens. Would I recommend them? Sure, if you want extra privacy and are fine with no ability to prove ownership of a domain might something happen.

I now have my domains at https://flokinet.is. A company based in Iceland. The site is from the '10s and the billing section is slow but they where mentioned as a privacy friendly option as well and apart from the transfer (I did things wrong with DNSSEC and they where a bit slowish with response, but mostly due to my impatience) I haven't had a problem with them.