When checking in in Hong Kong I avoid HK Express check-in counters even though you can use them for Hong Kong Airlines.Invariably when I go to check in the Hong Kong Airlines counter in Kowloon Station there is a small line but no one at the adjacent HK Express counter. Each time I tried checking in there they weighed my single carry-on, even when flying business class. The last time they insisted on checking my small trolley in which I had put my backpack with computer. So I stepped back and unpacked everything. With no one at the Hong Kong Airlines counter I went up there to check my trolley and it weighed under the limit so the agent told me to take it on board with my backpack.

So, in my experience Hong Kong Airlines has not been very strict on this but HK Express absolutely was.