Facom 603F, aluminium and I think stainless attachments and inserts for preventing rust.
In theory is a a bit heavier than the 601 however I cannot feel the difference. It feels very strong and sturdy.
The blade attached by spring loaded mechanism on the front that makes it study and not rotating while changing blades. The 601 has no rotating attachments so a bit more straightforward when blade changing.
Very tight tolerances of the rear blade attachment with positive and easy locking at 45 degree intervals.

All in all very pleased. I would prefer the handles to have a bit rubber texture as the 601. The aluminium 603F feels very cold when getting it on your hand[emoji4].
NO COO!!![emoji15]
I am not generally buy facom for that reason with some exemptions, of course[emoji16]