Sanfax, it’s not a scam, but an exaggeration. If you use a Heloc as checking/savings account, you can of course save on interest expenses. But it all depends on how much money you usually hold in your check and savings account. If you have a lot of money sitting, it could be good strategy.
But realistically, if you have a $800k mortgage, if you want to pay off in 5 years, that’s $160k payment every year just for principal. Plus interest, you will need to pay close to $190k per year. Most people do not have this much after tax and after spending income.