The doro is the sihoo I-have too, they are similar in design yeah but the Flex has a much better backrest that's more ergonomically focused with automatic adjustments and fine tuning.
It's very comfortable I have to say, the backrest especially so thanks to the auto adjusting lower back bit. The adjustment of tension on the reclining is also nice, can gently slouch back and it just glides back to rest without having to put effort in etc.
The thing I don't like is that the arm rests are a bit high even on the lowest height setting by about half an inch so when I tuck myself into my desk and working upright, the armrests bang against my desk edge as they are not low enough to slide under the desk which is how my old ThunderX3 chair would operate nicely. To work around this I need to use thick washers on the bolts that attach the arm rests to add the extra gap.
The other is that whilst the legs, whilst nice, are sharper than I would like on the very ends, which means stubbing my toes on them could be an issue
Otherwise the rest is quite great really I have to say and there is plenty of adjustment for all of the important areas. I'm liking the mesh too, first time using a mesh chair with these two. No more hotspots