a quick update:
finally gotten my Sihoo M57 from Lazada few days back, free shipping from the seller to east M'sia, save me quiet a lot on the shipping fees there as most seller is charging couple hundred just for shipping huge item like chairs
Total damage: RM799
I was at work when the parcel arrived, and my 13 yo son took the liberty of assembling the chair for me

I was impressed by the quality of the chair, when you mention china chairs, ppl will first thought of poor workmanship, like some cheapo gaming/office chairs I've bought before, all are wobbly even I've tighten all the nuts
but not this M57, even after assembled by a minor

, it's pretty solid
FYI, I'm 100Kg+, and doesn't feel any loose parts at all, no weird squeaking noise here and there, I was very skeptical to lean fully back also, as I'm heavy and really scared the chair might topple
and the fear was unfounded as well, it took my weight full lean without issue, it is quite balanced
I'm suffering from back pain as well, the adjustable back support is a god send, never before I have a such a good back support
adjustable armrest also is great, happy with it
overall a 5/5 rating for this chair
thank god I didn't go buy those overpriced gaming chairs