I was not impressed. At first glance, it looks heavy (22+ kg), solid and sturdy. It doesn't creak, it doesn't wobble. Assembly is very easy and doesn't take more than 15 minutes. Theoretically, it supports up to 150 kg. Various (usually paid) reviews claim that the mesh is durable and doesn't wear out after 1 year, a problem that is not uncommon in chairs of this category.

However, after 2 days of use, I just can't get used to it, it's quite uncomfortable because:
it presses on the back of the thighs, the seat is wide but also relatively "short" (that is, the legs stick out at least 5 cm more than I'm used to even if I pull the seat all the way away from the backrest), also in an upright position it is almost impossible to rest your head back unless you sit like a Buckingham Palace guard and have 0% kyphosis, the backrest only locks in 2 positions (one completely uncomfortable middle and one quite reclined that is only good for sleeping) and the armrests could be further apart from the chair, since when you rest your arms on them you feel cramped.

The lumbar support seems quite good and covers the entire lower back down to the glutes.

But the worst thing is that to lean back even a little (say 5 cm), the backrest is very stiff and you literally have to use force with your legs no matter how much you weigh... and you have to keep pushing for the backrest to stay in the reclined position. And it's not just me who finds the chair overall uncomfortable, but even my wife who is half my size (see: she passed it on to me and kept the old one).

At 200 euros, which is now the price of the black model (on discount, since the manufacturer sells it much more expensive), it might be a good option for someone who finds the chair comfortable. But the 250+ for the white model I almost regret. The 4 stars are completely generous, I will change them to 3 if after about a week I still can't get used to it.

update after 1 month of use: I've somewhat gotten used to it and will generously keep the 4 stars, but I've tried much more comfortable chairs in this price range. It is still uncomfortable and tiring for the arms (especially the ulna area) when sitting in a slightly reclined position, because the armrests are very hard. It is uncomfortable and narrow in the thigh axis when sitting completely upright, so you need to recline slightly backwards. Therefore, forget about locking the backrest in the upright position. The head rests properly on the back only when you recline slightly, but if you manage to find the right position then it is a pleasure (but this means that the computer screen must be raised higher than what I'm used to). Generally, I remain unimpressed and wonder why my review is getting 2/5 so far when no one mentions anything contrary to any of the above problems. Personally, I have found it comfortable only when watching something on YouTube, but not for work, browsing, gaming, etc.

update 2: on the purely technical features I agree with everything user Thanasis_Grammatikas wrote in his review (especially about the shirt lifting up when you move...), however I still find the chair marginally comfortable even now that I have gotten used to it. Yesterday I tried a chair at half the price at a well-known Swedish department store and honestly found it MUCH more comfortable and relaxing, at least in the 5-10 minutes I tested it. This doesn't mean it was overall better, because it doesn't have the same build quality, durability, etc., but from the Sihoo S100 I expected more at 200-250 euros.