His debuff offense down and counterattack can help to tame rey, and his AOE can finish toons that are just barely hanging on.
Ig100 is a bit of a liability against ST Han, like any low damage counterattacker.
Ig100 is viable at 5 stars and g8. Health like a 7s g8 phasma. He hits for 2-3K crit, and crits for 1.5-2K on his AOE. His O Down lands about 50% of the time, so far. It works on Raid bosses, too, up to tier 4, anyway.
The TM on his AOE doesn't seem to land very often for me.
Adding him to the team has created a lot of much longer matches with interesting finishes, anyway. I wouldn't say he is greatly improving nor greatly hurting my squad, subbing him in for a glass cannon. It's just a tradeoff of DPS or debuff/counterattack/high health. And his AOE is not so low it's useless, anyhow. I may have dropped a couple extra ranks, simply because of the novelty of my team and the low power ranking (have a couple low star toons on there, yet). But he looks to be viable. Especially on a time-sinking tanky Arena defense team.