Salary packaging in Australia

For computers/phones: seems like income tax and GST are exempted (for one personal electronic device per year, if it is intended for mostly work-related use)?

For cars: It seems like there is an arbitrary threshold of 20% of the initial purchase price. You bundle up all your private car related costs (like fuel, insurance, finance, whatever), and each year you pay up to that threshold from your normal income (as a post income tax contribution which is needed to exempt the employer from Fringe Benefit Tax), but everything in excess of that threshold is exempt from GST and income tax?

(The catch seems to be a regulated repayment schedule, providing opportunity for exorbitant interest rates and fees?)