A kellendu is not considered a suthra weapon; instead it's considered a companion. A character would still need Suthra Training to train one to obey various commands (the Specialization would be "Aides & Companions) and would still need Suthra Use to issue those commands or exert control over the kellendu.

If a character wanted to purchase an already trained kellendu and use him for hunting or in combat, then Suthra Use would be sufficient. But this would mean that the character could not train the kellendu to obey any additional commands (unless they purchased Suthra Training or took him back to another trainer).

But generally, if the suthra is used mostly as a substitute for a melee or missile weapon, then it's considered a Suthra Weapon proper. Otherwise, it's just a trained suthra aide, companion, or mount.

It occurs to me that I didn't address the actual world differences between suthra weapons and suthra used as companions or mounts. The key difference is intelligence.

Suthra weapons have been specifically bred to be really good at performing a few tasks (either offensive or defensive depending on the variety) but otherwise have fairly low intelligence and would likely die if left on their own. Kellendu or chinti, by contrast, are quite intelligent, able to survive in the wild on their own.

Suthra weapons, in general, are not considered pets by the Zoics, no more than say, a pistol would be considered a pet (although some Zoics can develop an affection for a suthra weapon just like they can for a beloved sword or gun). Suthra weapons generally do not have anything even resembling a personality, although some might develop quirks (such as always wanting to rest in a certain area or preferring a certain type of food).

Kellendu, OTOH, were bred to be pets and companions. They can also be used like guard dogs or as hunting dogs. They absolutely have personalities of their own and are extremely intelligent. Same with most riding beasts, although some are more difficult to train and less intelligent than others (buthan, for example, are not the sharpest tools in the shed).

Hope that answered your questions!