I feel like weapons benefit less from ISS when they cost less ink (I've heard a rumor that weapons with a higher ink cost get reduced more by this ability, which is only sort of true, because the subs reduce it by a certain percentage. Since some subs use up larger quantities of ink, a greater amount of ink gets reduced, but it doesn't actually take off an even larger percentage than it would with a weapon that consumes less ink, which is what that statement originally led me to believe). The number of times you can use them can increase, but you don't ever need to use any of the small ink consumption subs consecutively except for maybe with burst bombs, making ISS somewhat useful with it in some situations, although they aren't that deadly, and you shouldn't rely on them to get you kills, especially after the update in which their ink cost increased to 40%. The worst subs to use ISS with are probably disruptors and point sensors, because they consume a smaller amount of ink, and ink mines, sprinklers, and beacons, since you generally don't need much ink immediately after placing one, and the ink mines also don't consume much ink, making them the worst subs to use ISS with (They're really bad, so that shouldn't disappoint anyone). It can be useful with other bombs and splash walls because you have more time to use your main weapon after firing, and those weapons are frequently used against enemies, so after using the sub, you're much more likely to actually need the extra ink.
I think there are much better subs you could be using. I'd say you absolutely shouldn't use this except with Suction Bombs, Splat Bombs, and Splash Walls, and even then I'd strongly advise against it. ISM(ain) saves ink in more situations since your main weapon is used a lot more than your sub, and when you do need to use a sub weapon either just before or after using your main weapon, you'll save some ink no matter which type of Ink Saver you're using.