Why mirrors exist
Mirrors are how a Tor market survives attacks. Every mirror is a separate onion address pointed at the same backend, so knocking one address offline does not knock the shop offline.
A common newbie mistake is thinking the mirrors are different shops. They are not. Your account, deposits, orders and messages appear the same on every URL because they all read from the same database.
Read the access guide before picking a mirror. And if you save any of these to a bookmark, verify the URL against a PGP-signed rotation first.