Regarding rapidly paying off a mortgage, the sweet-spot is at around HKD 3-4m for your first apartment/boat, i.e. big enough to live in, but small enough to pay off reasonably quickly. This also reduces the risk regarding prices, because if you are paying off almost 0.5m a year, it is hard to be left in negative equity for long.
My first apartment was around 3m/1200' and after about 3 years and paying off over half the mortage I bought a bigger place 8m/1600'. I remortgaged the first place up to brake-even point on rental income (back to 3m), and then used the remortgaged amount to pay the 10% deposit, mortgage insurance, stamp duty and reno cost for the new apartment.
This is the hypothetical case that would get you sacked and was alledgedly the case with the sacked FO's:
Both parties bought an apartment each (his and her's) and individually claim full owner occupier allowance to cover both mortgages. You can do this without contravening the T&C's of the housing scheme, so long as you remain an owner-occupier, and you are not married to the other person. If you are a married couple, only one party can claim the full allowance.
They move into the bigger apartment together and rent out the other apartment to a third party, while still claming owner-occupier assistance on both apartments.
In this hypothetical case the person not claiming the full allowance could have claimed the 24k basic allowance, but chose not to go this route and continued to claim the full allowance.
This doesn't comply with the housing scheme conditions, and would result in the company being out of pocket about 20k per month.
Last year Personnel announced an amnesty last year listing the types of abuses that might be occurring and offered a few months leeway for people to own-up and come to some arrangement to pay back any excess payments to the company. I can only assume that the people involved did not take this opportunity to come clean, and were found out.
My opinion is that the housing scheme can be used quite legitimately as a get-rich scheme, and the owner-occupier option is superb if you are not too risk adverse. There are enough 'allowed' ways to use the scheme to your advantage, that you would have to be crazy to try to pull a fast one on the company.
They are not (entirely) stupid, and it only takes one jealous person to grass you up...