(if you've) seen one, you've seen them all

US /ɪf juːv siːn wʌn, juːv siːn ðəm ɔːl/
UK /ɪf juːv siːn wʌn, juːv siːn ðəm ɔːl/
"(if you've) seen one, you've seen them all" picture
1.

si has visto uno, los has visto todos, todos son iguales

used to express the opinion that all things or people of a particular type are very similar and that there is no need to see or experience more than one

:
I don't need to visit another art gallery; if you've seen one, you've seen them all.
No necesito visitar otra galería de arte; si has visto una, las has visto todas.
All these new cafes are the same; if you've seen one, you've seen them all.
Todos estos nuevos cafés son iguales; si has visto uno, los has visto todos.