Hi there, your friend is totally wrong, allow me to explain 1st of all savings accounts tend to offer a lower rate than your mortgage account and secondly you may be liable to pay tax on your savings accounts. With reference to repayment vs interest only this is totally dependent upon 1) your business plan and 2) long term objectives... ie. if you intend to retire and use the rents as income supplimentation then you may be better of with repayment as the mortgages will be paid off on retirement so then all the rents are profit minus tax of cause.
Now if your objective is to buy more and more investment properties then you may want to consider intererst only as you will need every extra penny towards future deposits.
Also are you going for capital growth or income today or income in the future? Capital growth = interest only.. income today = interest only... income in the future poss within retirement = repayment...
As you can see its hard to advise without knowing what ones long term plans are.
Hopefully ive helped you.
Alex M
www.oakhillmortgages.co.uk