March Mutant 8: Polyominous / Quad-Wrangle (cipher)

In this Polyominous puzzle, every region must be shaped like a rectangle. (Thus, the puzzle is similar to a Quad-Wrangle puzzle, but without the restriction that every region must contain exactly one number, and with the restriction that regions with the same area may not share an edge.) Additionally, the given numbers have been replaced by letters; all instances of a particular letter represent the same number, but two different letters must represent different numbers.