I myself main the jr and think it's an amazing versatile weapon.
quicker TTK than the Aerospray
Crazy Ink Efficient.
probably the most useful bomb weapon. Able to ricochet, explodes fast enough to catch some off guard and at the least can control a hallway for a few seconds. you can use it to kamikaze in a bad situation much easier than you would be able to with a suction bomb
Bubbler is your free "oops" button, though some are able to counter it, you should be able to recognize who is going to be able to counter it or not. use the invincibility to retreat if you're up against a smart opponent.
The bubbler can be used to push. If you round your whole team up and bubbler then they all get it. while one jr with a bubbler is an easy problem to deal with. a .52, tentatek, or squelcher with a bubbler is a nightmare and can quickly change the tide of the battle.
Yes, the accuracy is bad, makes the weapon fit more into an ambush playstyle, or forces you to use grenades to force a player into your favorable range
You won't win many face to face encounters, but that's one of the best things about this weapon. When I find myself playing the tentatek, or the .52 I end up challenging my opponent's range and getting splatted. the Jr. has VERY clear limitations that you need to be aware about. the gun makes you think creatively. what walls can i swim up in order to catch my opponent off guard? where will they be forced to run to if i throw a splat bomb there? This is not a gun for a soldier, you cant point shoot and win. It's a gun for a general, a strategist. Coupled with a great creative mind the gun has the tools to control the flow of battle further than merely splatting enemies.
also the ink efficiency and coverage is great in turf war and splat zones.