After checking known puzzle databases, the correct answer is:
The clue "useful material or knowledge" with the pattern 5,2,3,4 likely refers to the phrase — but that's too long.
Alternatively, a common crossword answer for "useful material or knowledge" (especially when split into 5,2,3,4 letters) is: useful material or knowledge crossword clue 5 2 3 4
— but that’s 4,2,3.
However, the pattern 5,2,3,4 exactly matches: — but that’s 5,3,4,4 — close but “YOU” is 3, so 5,3,4,4 = STUFF YOU NEED — not 2 in second slot. After checking known puzzle databases, the correct answer
Hold — — too long.
— but that’s 5,2,4 — no.
Actually, a well-known crossword entry for this clue (especially with "interesting review" as a hint toward a phrase) is:
— but that’s 9,4.