Cad is great for high single-target damage, particularly against Jedi, and for his guaranteed stun (unless resisted). The stun component works on all targets; only the turn meter reset is limited to Jedi. I just brought him in for a couple of my Galactic War matches this morning to shut down a very dangerous 5* Dooku long enough to kill him; stuns are perhaps the best way to deal with heavy counter threats, and Cad has one of the most reliable in the game.
The problem is that Cad's upgrade shards only come from packs, which means you won't be upgrading his star levels without spending $$$$, and he's very squishy at say 3*; most of his item upgrades improve his damage output, rather than his HP or toughness. He's very useful in some circumstances, but might be hard to fit permanently into a high-level team.