So I tried this out for a bit tonight.
I like the Splash-O-Matic; it fires fast, doesn't have much spread and has Suction Bomb Rush (and of course, Suction Bombs). After toying with the Tentatek Splattershot earlier and loving basically everything except the Inkzooka (it's good, but I'm not really feeling it), this looked to be my new favorite weapon.
Afterward... Well, I like it, I could see myself bringing it out from time to time, but I'll probably stick to Tentatek and .52 Gal Deco for now.
I like the shooting, it has enough spread that it can sorta compensate for my crappy aim and it's pretty fast. I like the Suction Bomb, it's my second-favorite sub weapon to use (Seekers will always be first for me). I like Suction Bomb Rush, it's like Suction Bombs but more (well, that's actually all it is, but I still like it) and I felt like I got it fairly quickly, which is nice (but could have been my gear, think I had Special Charge Ups on my shoes).
But I don't love the weakness, it keeps me from winning firefights up close that I could have won with the Tentatek. And I don't love the range, which doesn't feel long enough and keeps me from winning firefights I could with the .52 Deco.
Overall, definitely flawed, but it's got nice strengths and feels like it fits my playstyle, so it's a keeper for me, even if I might not pull it out too regularly.