Every unit higher is meant to represent 10x the production in universe.
The game's actually a bit mixed on that front; order-of-magnitude production numbers make sense when trying to justify why two worlds that each produce 5 of a given thing are unable to supply a single world that requires six of that thing but are difficult to reconcile with market share being more or less [local production] / [sector production], especially in markets where something like a quantity-vs-quality tradeoff is unlikely (my size-3 Ore outpost probably isn't producing such pure ore that it's selling for enough to outweigh a several-orders-of-magnitude difference in production volume, for instance).
So, toxic planets are useless.
I wouldn't say that; Toxic worlds are one of the few non-Habitable types that can have Organics, +50 Hazard Rating for Toxic Atmosphere isn't actually that bad unless it's stacking with a couple other bad modifiers, and you don't
need to use colony items to make a colony profitable. Furthermore, even considering colony items, Toxic worlds aren't especially bad - with how picky Soil Nanites are, three industries compatible with colony items is usually about as good as you can expect for anything that isn't an airless rock, and there's also a decent argument for only putting a single item on each colony since Luddic Path cells are annoying and a couple developed colonies give you more money than you'll actually need anyways.
The problem with Toxic worlds as colonization candidates isn't that they're "useless" but rather that they rarely have resource deposits particularly worth exploiting and (unlike gas giants, habitables, and airless rocks) aren't uniquely suited to any of the current colony items, so they usually just aren't that attractive as colonization candidates unless you have an Autonomous Mantle Bore and they have all three of Ore, Organics, and Rare Ore.
