Even if you wouldn't eventually get him for free, he just doesn't do anything special enough that you'd miss him. Ninjas are cool and all, but the game forces you to invest other resources (like cultivation and awakening mats) to even use them effectively for most anything. But power is power. Redemption Merchant should be used mostly for power, in my opinion, and if you're getting ninja frags then it should probably be mostly people like Hinata and Kabuto that you can refine into Iruka frags that will also net you summoning/seal scrolls. Space-Time Shop has tactics option and thread - depending on where you're at, it should almost certainly just be used for one of those purchases, imo.