From what I've read, the M1 type mortgages can be good for people who have money left over at the end of the month after paying all there bills. They can also be good for people who have a fluctuating income every month
There are a few good discussions on the pros and cons of this product on the web, one I found was here:
http://www.milliondollarjourney.com/...age-review.htm
More specific to the Manulife offering.
On the same site, they break down the numbers:
http://www.milliondollarjourney.com/...e-mortgage.htm
To quickly summarize the Manulife One mortgage, it’s a giant HELOC that encompasses your mortgage, chequing/savings and other debt. The biggest advantages being convenience and the ability to have your extra cash flow working against the mortgage. The disadvantages being the higher cost relative to getting a regular discounted variable rate mortgage.