Overpriced and low-impact. It costs $4 and rarely causes more than $3 of damage. This is weak efficiency, you're paying a considerable amount of $ for something which doesn't hit much harder than Pop-Up Window and has much less long-term utility than $4 Kakugos or Border Controls. The kind interpretation of Karuna is that it's a slightly-upgraded version of Envelope, itself a $4 ice which usually causes a $2-swing (a fake Pop-Up Window).
Jinteki doesn't have a lot of cards I'd want to protect early with a Karuna, and those cards (Rashida and Regolith Mining License) usually work better early with low-cost end-the-runs like Whitespace or Vanilla. Karuna costs enough that you probably wouldn't want to rez this early on a central server unless you have some econ running by that point. Spoiler: as Jinteki you probably won't, your economy is usually the slowest and the least able to bounce back quickly from a $4 expenditure. Even Kakugo is hard to pay for sometimes and it is a Jinteki workhorse which produces considerable long-term value for a short-term tempo loss. For an extra $1, you can get a Saisentan which is devastating enough on early facechecks that you can feel fine even if it bankrupts you.
In my experience, Karunā is more about protecting centrals early than protecting remotes only. I agree that it's only borderline playable, though (even though I have it in one of my best decks – it's hard to find good early defence in Jinteki).— callforjudgement