Very inefficient at Thwarting, so let's disregard that from our analysis. If you could guarantee zero boost icons drawn, Havok would generate two damage per turn for the rest of the game, pretty decent for the price. That's going to take some work, though - typically zero boosts are only around one-quarter of the encounter deck. Every boost icon drawn is 1 damage for 1 Ally HP, which is a bad rate, especially for an expensive ally like this. Further, it's unpredictable, so you'll run into damage waste and/or lose your opportunity to block.

(If you do have a way to guarantee zero boosts drawn, you might be better off just giving those to the villain for their activations.)

Outside of zero boosts, the ideal case would be something like attack for 3 twice, then block or attack for 5, which is decent value. More common would be attack for 4 once, then attack for 4 or block, which is getting a bit below average for output of an ally at this price point. And against harder scenarios, it won't be uncommon to see one attack for five and that's it, yuck.

Perhaps a bit better if you can upgrade his HP, as the first attack or two will be safer. You're still going to run into situations where you have to block early or risk losing your block altogether.

Might be best in a "To Me, My X-Men!" deck, to bring up your ally count so you're less likely to whiff. You hopefully won't kill him off on your "surprise" activation, but even if you do, it was still 5+ damage for 1+card, which isn't awful.