He is one of the best units so far. With his long range he is able to attack all enemies on the screen at once, most of the time. If it's a weak attribute enemy, he kills them with one hit sometimes. (If max pills + possible buddy skill: over 1000 Dmg) With his Ninjustu he deals over 3000 Dmg with a chance of immobilization, which buys you 2 additional turns.
Now he has the highest attack value for a long range unit and does with his Special over 9000 - 10000 Dmg (depends on field skills). Because of his range he participates in most of the attacks to deal additional Dmg. When doing a 25-Chakra cost emergency mission, he is able to reduce with his Special 50% or more of the bosses health.
High attack value for Long Range
Ninjutsu has a chance to debuff enemy
Does a lot of Dmg with Special
Field skill may keep your attack value without a debuff
Able to attack all enemies most of the time
His Ninjustu and Special do only single target dmg
Low Attack in comparison to other 6* units
Buddy skill won't be used much cause Gaara is a unit for the first row
Special with high Chakra cost (need to stall sometimes)
Thanks to VynnIce for his awesome evaluation notes!
I would recommend 6* Naruto at first if your team cost isn't high enough, because of his buddy skill Gaara will get his Attack boosted by 115, instead of 95. 6* Naruto is also a very nice unit for the first row, if you change him with Gaara other teammates will get a Attack Boost by 80-160 with his Field skill. Not only that, he makes also a lot of Dmg with his Ninjustu and Special.