Thats what Ive heard also, once you pay it off,the protection goes away.The merchant has their money and the card company doesnt have any 'leverage'.
One thing I do, is I use two different cards.Make sure the 'closing' date is opposite. (the card company will change the date if you request) .
Then switch twice a month, which card you use. This way you extend the time you have to pay, and also the time of "coverage' .should you be displeased.
Let's say you wanted to but a 'large; ticket item, I wait until the close date, and buy the next day, this gives you extra time before it even hits the card, or you get billed. then when you receive the bill, you have a few more weeks to pay it. In some cases this extends it out almost 30 days.
I had a Penny card 30 years ago I cut in half, and sent back with a letter .(return res.). But to this day it shows on my credit rating. and they continue to call and make offers ,even though I told them I had cancelled 30 years ago.
I did use the home depot offer once, almost a year with no interest and payments. I didnt have any trouble. I got 11 months no payment or interest, Paid it off in full a month before I had to.They depend on people defaulting on the payment at that time, and can charge back the interest.
Good Luck to us all this season.
Al