TLDR; at the end.
Mini splatling seems better than it's heavy counterpart. It basically has an increase in range and power with it's sub and special, so I'll probably highly recommend having special charge up if you don't already do.
I strongly disagree, you are underestemating the Heavy Splatling and it is not that easy comparing these two. You are right about the Special Charge though.
The Heavy Splatling fulfils an absolutely different role, so you can't just say the Mini is better. But if you still want to compare them like that: In most cases the Heavy should kill the Mini due to the range. A single bomb and a limited Special will not completely make up for the loss of range. Also: The Heavy Splatling is a more defensive weapon and should make use of its Splash Wall, whereas the Mini Splatling is way, way, way more aggressive. And do not forget: A skilled H. Splatling user is able to close combat with his H. Splatling, too.
But to the topic itself: While I myself love the Mini SPlatling, I do think that there are only few reasons to really use it.
1. You're a Splatling main, therefore switching between Heavy Splatling and Mini SPlatling is a bit easier than between Heavy Splatling and Tentatek.
2. You're bad at using the Heavy Splatling but want to get into Splatlings -> The Mini Splatling is a lot easier to pick up.
3. You just want to use it becase you just want to have fun - and this is absolutely fine.
Now let's come to the issues I see:
First of all it does not fulfil the role of a Heavy Splatling. Now while this is in general not that big of an issue, I'll come to this later.
Its stats are way too close to the Tentatek. It has almost the same time to kill, it has only slightly better range but it is less mobile and it has to charge up which the Tentatek does not have to. Yes I am aware the charge is really short, but that doesn't change the fact, that the Tentatek does not have to charge at all.
Last point: It's loadout is the Tentatek's.
Now let's look at the real problem: It is basically overshadowed by the slightly more efficient Tentatek. They will most likely fulfil similar roles due to the Mini's aggressive nature and the really short range. Therefore, for most people, generally everyone who is used to Shooters, the Tentatek will most likely be the superior choice. Now the problem is, you can't use it like a Heavy Splatling. The Heavy favours a more defensive playstyle with its long range - someting the Mini can't.
Therefore why use the Mini when the Tentatek exists? It's as easy as I mentioned above: Easier switch for Splatling mains, you want to learn SPlatlings overall or you just want to have fun.
I will say it once again, I LOVE the Mini Splatling, it's great to see how different it is from my beloved Heavy SPlatling, and I am definitely going to use it myself, as it's a bit easier to switch between to weapons of the same kind. But I think for most people, the Tentatek would be the better choice.
This will however change as soon as the Zink version gets released. For now I am convinced that the Zink version of the Mini Splatling is going to be the REAL Mini SPlatling gun.
Edit: I might, of course, be wrong since it has not been 24 hours since its release, but right now, this is how I view it.
By the way, there is a typo in the thread's title. It should be SplaTling with one t.
Edit2: Also Aceofscarabs listed some nice points in his/her post.
TLDR; It's a Tentatek for those who main Splatlings, its a lot of fun, it looks great, the Zink version is going to be awesome. But don't overestimate it because you want it to be "the best weapon". It still plays different than a Tentatek, though.