Actually I am one of those players who used this feature in early games. haha

I am one of those who do not fancy treassured ninjas that much that is why in early games I tried exchanging seals for kurenai full BT, Yamato Full BT, Guy Full BT and lee BT. I know for others it is such a waste, but for me since I have better plans for my future lineup (not planning on using seal treasure ninjas for my main lineup) I just fast forwarded my useful ninjas breakthroughs. [ Now more treasured ninjas are getting BTs so things get a little bit interesting with seal scrolls ]

This tsunade NPC helped me a lot in early games to get ahead of 9tails/Summon 40cps. I have used Choji as my lineup before so MB+Choji GNW+kurena+Hashi helped me through my daily item grinds.

Now for me this NPC Tsuna is not that useful anymore, but to others I think they can come in handy :)

Altho upgrading this feature is not a total loss, we shall see I guess.

Actually I like the idea of this post, overall. Since normal vials are expensive hehe. It would be nice to see some updated books there :)

Oh boy that book is expensive in coupons value. I really hope I can setup my ninjas' BT before we get that update (if ever). :3