Cat 0 comes on them from Deere...
The Cat 1 has bigger pins, and wider spacing between the lift arms to accommodate the larger implements.
There are getting to be less and less Cat 0 attachments available, and a few guys have converted theirs to Cat 1 because so many more attachments are available that way, and some are cheaper than Cat 0.
Bill Reugg offers it as an option on his 3-point kits, or at least I know he used to.