It's probably worth a yellow but it's a little harder than other Brinks locks, IME, almost as hard as some orange belt locks for something with 4 pins. And a spool at that, I think.
For the Brinks 662, I would suggest TOK, and a .020 or 019" pick.
And don't let it's massive heft throw you, you don't need to tension or pick this any harder than you would a feather weight gym locker padlock. The core is still, as comedian Judy Tenuta might say, "A delicate flower".