I don't know about HK laws on laser pointers but here in Australia there are restrictions on laser pointers - anything >1mW requires a permit in most states, without a permit you're liable for possession of a prohibited weapon whether or not you planned to use it. Even <1mW, you may be required to have a reasonable excuse for possessing it if you take it into a public space (at least in some states, I haven't checked all of them).