Adding many 4/2 Bloonjitsus are extremely reliable against distracting Ceramics and lower bloons, especially in Freeplay Mode.
There is no reason not to get the Path 2 upgrades because these two upgrades are both really useful for providing both accuracy (via Seeking Shuriken) and a high chance to distract bloons (via Distraction)
Since DPS and shuriken accuracy via Seeking Shuriken are generally more important than a spray of shurikens with a chance of distracting bloons via Distraction, it is best to go along Path 3 instead of Path 2.
Bloonjitsu Ninjas are among the best candidates for Berserker Brew and Stronger Stimulant, even after the Version 6.0 Alchemist nerf. This is because they don't shoot so fast as to expire potions so early but at the same time shoots many projectiles at once with good overall pierce and damage.
This upgrade used to be indirectly cheaper to get in BTD Battles Mobile thanks to Sharp Shurikens and Double Shot getting their prices decreased. However, since update 4.9 the overall cost to get a 4/x Ninja Monkey is now the same as in BTD5.
The Bloonjitsu can shoot every 0.42 seconds without any bonuses from the Monkey Lab.
The cheapest possible 4/2 Bloonjitsu in BTDB Mobile normal battles is $4500 in between Version 4.1-4.5, obtained from discounting the original price of $5000 ($500 + $300 + $250 + $250 + $400 + $550 + $2750) by a Village.