Such loans are usually quite flexible and many banks offer very attractive rates due to intense competition.  Because the line of credit is secured by a second mortgage, the interest rate is usually lower than other forms of credit.  It sure beats maxing out your credit cards.

As far as I understand,one finally is left with mortgaging two properties instead of one.The property you will buy is automatically under mortgage.

We are talking here only about one property and not two.  It is a 2nd mortgage on a already-mortgaged property.