Are mortgage checking accounts (MCAs) legit?

[pr0crast]

http://www.sydneyfinancialgroup.com/

My mom mentioned this to me. Apparently they have done this in other countries like Australia for a long time. The way it works is if you have a 200k house and you take a loan out to pay it, but you have 120k in your mortgage checking account, you are only paying interest on 80k of the house. If you withdraw 50k from your checking account, then you are paying interest on 170k of the house. Traditional American mortgages, you pay interest on 100% of the loan value for the entire term of the loan.

Legit or no? Anyone use one of these things?