As is the case for many things, it's just a piece of paper that will open doors for you. Your experience and your background will dictate what jobs you will be doing.
There's no doubt that the best place to be in HK is an international school preferably one with an IB stream since you get another piece of paper making you more marketable. If you manage to get in ESF or one of the top tier schools like CIS, CDNIS, HKIS, GSIS the wages and benefits are better and the quality of students also tends to be much higher. The downside in some of those, it comes with more pressure, more work and scrutiny.
If you know your stuff in IT and that's what you want to teach, you'll get there. The piece of paper simply allows you to be hired. I worked for over 20 years in education, more than 10 in HK, in that time, I taught less than two years for what I was initially certified because I had other skills that were more in demand. When I was involved in the hiring of teachers, I always looked at the set of skills and personality they brought in order to see where they could fit best and how much flexibility I would have with each individual. Pieces of paper and skills are often two different things...