适于 is more formal/written than the colloquial 适合 (shìhé, 'to suit'). You'll see it in product specs, scientific writing, and policy documents — e.g. 适于儿童使用 (shìyú értóng shǐyòng, 'suitable for children').
grammar
于 (yú) here functions as a literary preposition meaning 'for/at/in'. Pattern: [thing] 适于 [activity/use].
