Lived there a spell and still get there every so often. Really safe place, no muggers, only troublemakers are drunken "Gwailohs" (foriegners). Bar brawls are settled with fists.
Your biggest threat will be pickpockets working the crowds, but HK has a tourist crime compensation program whereby you can make a claim for reimbursement if robbed.
If there ever is an altercation with local criminal elements (Triads), concealable knife will not be of any help. HK Triad members will be many, will be better armed and will swarm you. As long as you don't go around picking fights with locals, HK is a very polite and safe place.
HK's general law makes illegal any "sharp or pointed weapon" which is so open for interpretaion that you really don't want to get caught importing anything.
If you really want a knife, buy one there at any of a million tourist shops and throw it away when you leave. Suggest surefire/maglite flashlight to carry instead.
