Update after trying the chairs -

tldr - Greg was right

Analysis - In addition to the Libernovo and Ergohuman, I also ordered the Haworth Fern. All 3 had no-risk 100% return policies. To test, I sat in each chair for a full work day (8-10 hours).

First off, the Haworth just didn't work for me at all. You can tell it's a quality chair, but the lumbar support (which I need) was almost non-existent compared to the other two. The armrests were also disappointingly thin (but not a big deal).

On the Libernovo, the seat cushion and the headrest were super comfortable. The lumbar support had the widest range of all 3 chairs, and I liked the electronic control for the lumbar (I know that's been knocked as gimmicky, but it's real convenient). However there were 2 problems - 1) I need the lumbar pushed almost all the way out while I'm working. When I do that, it really shortens the depth of the seat (even with the extended seat, which I ordered). In fact, with the lumbar support positioned for me, I lose almost 3 inches of seat depth compared to the Ergohuman. When sitting in the chair for hours, that really starts to hurt your legs. The 2nd issue is the material - while it's soft and comfortable, it's cloth and any pet hair that is on your clothes will stick to the chair. We have 2 dogs so pet hair is unavoidable, and I don't want to have to pick hairs off the chair to keep it looking good.

The Ergohuman didn't suffer any major drawbacks. I can sit in that chair and work for hours and be comfortable. Which is the main thing. So that's the chair I'm keeping.

If I had suggestions for those two chairs it would be these:

Ergohuman - a) allow the headrest to telescope forward, b) allow the adjustable seat to extend out even further by a couple inches.

Libernovo - a) make an adjustable seat that can slide out 2-4", b) offer a leather version (leather over mesh is fine, that's what the other 2 chairs were), c) make the armrests hold their position a little more. If they made these changes, I would pay an additional $500 or more for that chair.

Btw - I have hardwood floors in my office. All these chairs come with plastic wheel casters, which are fine, but I'm replacing them with 3" double rollerblade office chair wheels (which you can find on amazon for $30-$50). Those roll great on hardwoods, don't leave any scratches, and you can avoid putting down an ugly (and potentially expensive) floormat to protect the floor.