As an owner you will need to pay:
Government Rates and Rent (maybe $2500/qtr)
Management fees ($1.6/sqft/month in DB)
Income tax on the allowance (max 16.5%)
All of this will need to come out of your salary, as the housing allowance can only be used to cover the mortgage costs.
You can set your mortgage payment to the housing allowance ceiling, and lock it in for 2 years. On the size of apartment you mention, it will pay off super-fast.
It is a bit of a sore point that CX PNL insist to the IRD that the housing allowance is a cash allowance, so is considered as taxable income, even though it is not strictly speaking cash - as you must spend it on mortgage/loan repayments. Many owner-occupiers have questioned this in the past with the IRD but CX PNL insist it is cash.
I think there is mileage to push this matter further, but I am reluctant to bite the hand that feeds me.
