Very stable once constructed. Bit fiddly to put together, but as already said, don’t tighten up until all bolts in place and DONT cross thread bolts !  I found it best to put seat face down (straight legs on floor) and do one side at a time to tighten . 
Only negative...one of bolts was not pressed properly and so we can’t construct last chair until we go to b&q for new bolt..if they have any .
Otherwise, very happy..