And the atmel product is 12x out of reset, so it compatible without fiddling with any registers or parallel programmers.
so is the Rx2H.
From your other post, the "66x" does not have 8k !. The 668 does. The 664 and 662 do not.
That's why I wrote up to 8k

The two previous posts state why a manufacturer would want to make a 6x/12x chip, that I understand, I asked "why would a user want to alternate"

Erik