you're thinking of storm flip, and no. There are multiple differences. Its a smoke type cloud; not an expanding dome, so it conceals anything inside it and damages them. It doesn't actually "summon" the storm.

Just does damage to health instead of shields similar to how the storm works, and the whole "storm particle" spiel was to explain (lore-wise) why caustic wouldn't be immune to it's effects.

It's just simply a short acting gas grenade that does a small bit of damage to health and works in a small area, so it's designed for more tactical use and not for spam. But I also tried to give it properties that wouldn't make Bangalore's smoke or Caustic's traps/ult less useful, in order to make it balanced and fair.

So here's an example situation in which it would act differently from the other two Legend's abilities:

A team is camping high ground and you are trading shots, you carefully toss one up at them. If they don't move in time and get touched by the gas they take 25 damage to their health TOTAL (5 ticks of 5 damage, it won't go beyond that) which would be beneficial for a cheap hit, if they move to evade it, you can get a clearer shot or even cause them to give up high ground. Of course it has a lot of downsides because they are rare, only 1 per backpack slot to prevent abuse, and still leave the two afforementioned legends viable.

Or say you get into a fight and you shred someone to like 50 health (no shields), they shield up first (most people usually do), but you throw it at them and it hits. They automatically take 25 health damage (over 5 seconds). They're down to 25 health and just shields plus they had to relocate because they're in the gas (or they could stay in there blind since they're already taking the 25 damage), either way, the fight is now largely in your favor.

The biggest trade-off of this throwable is that the damage is capped at 25, and it's short lasting. But can be used tactically to drastically alter fights if you use it right.

In the first situation, Caustic's ult would be much much more effective and cover much larger area, still leaving him very viable. Bangalore's smoke could do the same, with a chance of hitting for 10 and still would cover a larger area due to the fact that it makes a wall with the 3 grenades that pop.

But it's a game changer for the simple fact that it explodes on impact, like thermite's, so if you have good aim, it will hit it's target. it also can be useful for less offensive legends to be able to complement their abilities to gain a slight offensive advantage, as well as make offense legends even deadlier.