If it is your own home and you intend to use it as an investment property later, paying the principal in to an offset account would allow you to redraw all the funds when it becomes an investment property later to maximise the loan and the interest deductibility. You can not do this through a normal P&I loan or a line of credit.
CBA have offset accounts. I understand you only get 100% offset if it is a variable home loan. Also make sure you also check out there "wealth package" as it could save you thousands depending on your circumstances.
Yes they have one called a MISA account. Minimum dep & w/d of $500.
As mentioned it is very useful should you wish to change from PPOR to IP at a later date.
It also saves on any redraw fees and can save on interest if used in conjunction with your credit card properley.