It's been discovered, over time, that Engolo is an Anarch (and minifaction) card in disguise. You rarely see it in Shaper (apart from the occasional Kit deck); shapers have all the best decoders (and thus can typically play something that fits their deck better than Engolo), tend to prefer to spend the early game building up their economy rather than running, and are often short of MU. You rarely see it in Criminal, either (although more frequently in Criminal than in Shaper!); if Criminals want an expensive decoder, they'll normally play Amina which has better numbers, and they have plenty of tools for early aggression other than icebreakers so Engolo doesn't have much of an opportunity to shine.
The thing about Engolo is that it's a card that's at its best when you need to run, but don't have a full set of breakers. It'll get you into servers early, which is nice; but it's also incredibly expensive at doing that, which rather puts a damper on things. The problem is that if you're using it for early aggression, you're paying 5 to install it, and more to use it, which leaves you at a low enough credit total that most of your economy doesn't work and you're at perpetual risk of getting blown up by Hard-Hitting News. Meanwhile, it's able to stand on its own for only a narrow section of time (the time before the Corp can manage to double-non-code gate-ICE their servers), and then is inferior to more normal breakers against the majority of ICE you'll face. So you're putting a lot in, and not getting enough benefit from it before it starts to fade in value.
A side issue is that Engolo looks like it wants to be a card for aggressive decks, but those decks often want to run – sometimes even have to run – lots of times in a turn in order to make their economy work. That isn't the greatest fit for a card which has "Use this ability only once per turn." stapled onto the reason why you'd play the card in the first place.
Still, Anarch as a faction has a lot of features that make Engolo a good fit. For one thing, they have no good decoders (except for possibly Buzzsaw, if you have enough support), so having suboptimal numbers is less of an issue than it would be elsewhere. Most importantly, though, Anarchs are good at keeping servers small; they have cards like Hippo and Devil Charm and Spooned to tear down a large server before it gets too large, and cards like Stargate to prevent the Corp drawing more ICE to replace it. But the main drawback of Anarch ICE destruction decks is that they often have trouble tuning themselves to the sort of ICE the corp is using. Being able to break ICE with Hippo needs an appropriate breaker. Being able to break it with cutlery requires knowing what sort of ICE it is.
Engolo fixes all that. "Hey", it says, "I know what sort of ICE you're facing: it's a code gate. I know which breaker you need: me." If you're only facing each piece of ICE once, having slightly awkward numbers isn't that much of an issue, but knowing for certain that you'll be appropriately set up for a specific piece of ICE, regardless of what it is, is really valuable. So Engolo is close to a perfect fit for ICE destruction decks, which can often rely on it as their primary/only breaker.
Engolo is also commonly seen in Adam, who has no breakers of his own, and who gets huge benefits from early aggression. It isn't as great a fit as in Anarch, but it nonetheless is a good fit for Adam's playstyle, often persuading him to import Engolo rather than something else.
As a side note, Engolo is really, really frustrating for certain sorts of Corp deck. Those decks are unpopular, so you wouldn't normally play it just to beat them; but Corp decks that heavily rely on cutting you off a particular sort of breaker (e.g. killers or fracters) hate having to fight through Engolos as well, and it works incredibly well against combos that rely on mythic or trap ICE.
Still, even if you're facing a more normal sort of deck, being able to make critical runs early is nice (even if you have to overpay to get past medium-strength ICE), and the numbers aren't even all that bad; Engolo is at its worst against the common 3-strength ICE (and loses out to Amina against larger ICE too, because it typically has 3 subroutines), but smaller and larger ICE is still widely played, and Engolo is one of the best breakers you could ask for against something like a Surveyor that's completely out of control. Engolo's become a little worse in the current upgrade-heavy metagame because it isn't that great when running multiple times a turn (which you'll need to be able to do against things like Anoetic Void and Border Control). But if you can keep servers small, the heavy install cost and frustratingly frequent need to boost will be offset by the fact that it'll carry you through much of the game before you find the rest of your rig.