Product review (3 stars): Edge of aluminum is burned by gas flame.
These fit precisely, the opening on the foil going right up to the edge of the opening on my gas stove.  And therein lies the problem.  At high flame (say, when you're boiling water), the flame hits the bottom of the pot and spreads sideways, contacting the edge of the burner opening.  This is not an issue for the steel of my stove.  But it is an issue for the aluminum; it heats up red and breaks down into aluminum oxide.  To prevent this, I need to trim these to increase the size of the opening.  If these were a permanent liner, I'd deduct one star for the inconvenience.  But these are disposable, so I'm deducting two stars, since it has to be done every time I replace one (and the whole point of this product is to be a convenience).  My recommendation is that they should offer a second, trimmed-back version for those that encounter this issue.