Let me put it this way.. They are available at regular rates; not the lowest rates. it makes sense if one is savvy about using it.. otherwise, it can become like a credit card with a huge borrowing limit and can increase the risk of one being over-indebted. The other aspect is that it comes along with a collateral charge mortgage and gives undue power to the lender if one has other unsecured borrowings from the same lender (generally banks).
Mortgage Agent, Broker Lic #10530