I tried out the version with point sensor and Inkzooka. I would say it's a bad weapon, because it's easy to compare it with the Splattershot pro forge: same sub and special. I would say you can more or less copy the H3 with the pro, while the opposite is not true. So, I would take the pro.
Of course it's not totally true. For example the H3 is more precise, and you can imitate a one shot kill of a blaster in some situations, and with quite the range. But honestly, in these situations, you would get a similar result from the pro.
Though I think it's not a good weapon, I would recommend it for learning purpose (A-S levels). In a duel, a good shooter player will shoot, swim, and repeat in very short succession, while a bad player will just shoot endleddly until one of the two players (or both) die. Of course there are lots of steps in between. If you use the H3 with the condition "I have to swim between two 3-shots", then you should be able to improve your movements in battle. Then take back your usual weapon, and go S+!
Not saying you can't be S+ with that, by the way. You can with every weapon.