Kisame will steal chakra and allows Haku and Kisame to unleash their skills same turn. Sai does ok dmg and summons block from 9-tail's normal attacks and it costs 0 chakra. Haku increases water attack and I also use water style to increase it further. Haku does a lot of dmg with water main so he is really good PVE. You may not do as much damage as the other mains but I have been at least in the top 10 lately. If you get strong enough to replace Sai - Sugetsu is a nice replacement because of his double attacks.
yes thanks for your answer^^ i already have half of fragments I need for him,I will get him very soon^^