The letters in the Montessori Movable Alphabet Game from The Persister Play Kit are presented out of alphabetical order to give your child practice identifying them by shape, rather than by memorized placement.
The Reading Skill Set follows a progression of letter sound introduction as a part of a whole set. With The Movable Alphabet, letters are removed from the storage case before your child uses them. As they build words, they'll use letters as needed, so it's not critical to be displayed in a particular order.