As the proprietor of a consultancy business I often include restrictive covenants in our employment contracts, primarily to prevent our consultants leaving and joining our clients directly, since in the construction / engineering business even the big boys are looking to cut out consultants and employee people directly to save a few dollars in HK. I know that, in general, these are enforceable in HK Courts as long as they are not too long in duration or too broad in coverage (ours often mention specific organisations and roles).
Having said that unless you are taking a large amount of business from your old employer to your new employer or poaching all of their staff, most employers understand that enforceability has its challenges and unless they have massive resources.
Finally, having been employed until around 6 years ago my personal and anecdotal experience is that much of what HR tells you is simply their 1 sided opinion and desire as opposed to the reality of the situation, primarily because that's what the Directors / Senior Management have told them to say to frighten timid employees into compliance.