Unbiased Mortgage advice

I like Jack Guttentag, the wharton prof who advises on mortgages in his webpage http://www.mtgprofessor.com. I find less bias in his advice. Here is a good tip:

Some borrowers are allergic to calculators and need a rule of thumb. Unfortunately, the common one that says "consolidation is profitable if the rate on the first mortgage is below the rate on non-mortgage debt", is wrong most of the time. Replace it with "consolidation is profitable if the rate on the first mortgage is below the rate on non-mortgage debt, and if the rate or mortgage insurance premium on the first mortgage is no higher with consolidation than without." This one will be right most of the time.

Full text is at http://www.mtgprofessor.com/A%20-%20Debt%20Consolidation/consolidating_with_new_first_mortgage.htm