I am smart enough not to have wasted 20 zetas for an ability that seems completely pointless, but when ever I face a squad with Vader who has that zeta I feel like it is entirely pointless to have! First of all there's so much ability block and stuns that it's so easy to stop Vader. If you use Titans you can stun him, if you use Rey with Thrawn you can stun him even easier...
Vader isn't a priority target so he's pretty much left for last or next to last in I'll order. This means he's almost always going to be stunned and ability blocked.
I feel horrible for people who literally wasted 20 zetas, the only thing that this may help with is his ships stats which really aren't even necessary to beat any squad out there. I would like to see the zeta reworked to add some other aspect, ability block immunity would be awesome. This way a Rey/Thrawn cannot stun him cause Thrawn's basic needs the ability block to apply stun. Or just make him immune to stun alternatively.
Generally speaking I'm glad I didn't zeta him, but if I had, I would have been mad because it would feel like I wasted zetas which isn't exactly the most abundant resource in the game.