I'd rate the Fern 4,5 stars if I could and 4 would be too low. Therefore, I'm giving it 5 stars in this form since only full stars are available in it.
When I first received and tried the chair, I didn't feel anything special about it. I know there are people saying it's great from the first sitting but for me that wasn't the case. I do sit a lot in very high-end chairs at my work and therefore I do have a pretty good idea of ergonomic office chairs. After a couple of days after receiving the chair, I woke up in the morning, got some breakfast, sat down on the Fern at my desk and at that moment I first felt that the chair is actually really comfortable to sit in. The feeling started to build from there and now after 3 weeks I'm very happy about how the chair feels and fits me personally. It makes me want to sit in it.
The adjustments available made it easy to set up for myself and I've found my favourite pose to sit in. The chair keeps me in a good posture and while at first I really didn't like how the recline worked, now I've found the optimal resistance setting for it and it simply feels natural.
I started noticing some upper back pain after around two weeks of use and I asked Haworth for extended return time to give my body more time to adjust, which they did grant me. I'm right now at the very end of that extended return time and I've basically made my mind to keep the chair. The upper back pain has started disappearing, which I assume is due to my body and muscles getting used to the new chair and better posture (which my old chair definitely didn't support) and this is exactly why I asked for the extension.
Basically the only complaint I do have (and which would validate the 4,5 star rating) is the lack of a headrest. A lot of people swear by on 3rd party (Atlas) headrest, but it was a poor match for me personally, so I'm in the process of returning the headrest to the manufacturer. Basically a good posture doesn't warrant a need for a headrest, but I'm playing VR games, mainly flight simulators, where I have to look around a lot in extreme angles and would want more support for my head and neck while playing. This is more of a personal preference though. I'm planning on making my own adapter to fit another manufacturer's headrest onto my Fern to remedy this issue in the future.
If my review appears negative, it's because it is honest and critical and there are no need for superlatives to fill in the actual user experience. The 4,5 / 5 rating is something I'd only rate a really good product or service and I do feel that the Fern definitely deserves it. 5 stars in my mind would require a product that either just naturally fits me perfectly or is tailored to my needs. In this case a good headrest included would've satisfied the first condition mentioned.
I wish you, good reader, that my review helps you in your decision-making.
-Joona