They couldn't even offer the $6 Burger for $6 longer than a month or so. They were almost immediately $7 or more. They were also supposed to be comparable to a sit-down restaurant burger. Somehow they cost more and are lower quality. It's cheaper to get a burger at Denny's than it is to get a burger at any fast food place these days, and it's a better and bigger burger.
At least where I was, when it came out it was $5 for the 'six-dollar burger', almost immediately after they threw in a bunch of other 'big' burgers. Odd that they tried to makr a 1/3 pound burger seem huge when McDonald's (at least in America) had been offering double quarter pounders for longer than I can remember.