not to be a dick, but before anyone goes rushing off to do this... do a search on it.
It's not the great deal it sounds like. Some countries have put the brakes on this and have it under investigations for false and misleading busines practices.
its not like you can ever go above the original amount owed on the line of credit. as you pay it down can you go back and spend that money? absolutely. does that defeat the purpose of the loan? depends on what you use the money for.
with the conservative approach of paying double, sure you can do that, but again, it goes back to your money earning 0% return and you not having the ability to get that money back if you needed it.
say you lost your job, would you be able to refinance and get that money back? no, you dont have a job. good luck getting a loan. with this you can draw the extra principal payments back out of the loan and use it to live off of. with traditional financing you would still have mortgage payments DUE!
look, its not for everyone, but if you have the discipline and the desire to acheive your goals its the most powerful tool ever made available in the United States. the product originated in Australia and there is a reason 60% of people in that country own their home free and clear.