Depends on what you want them viable for.
I've been experimenting with them. They can blast through most of the GW while ending at full health and protection, so that's nice. They are kind of like a Nihilus squad in that respect.
I am eager to get them to 7* so I can try them in the tank. I have a feeling they will fare OK in Phase 1 and 3. I didn't drop mad money on them to get them to full stars.
I also have a feeling they will make easy work of Light Side 9B, which everyone likes to complain about, but - again - I need more stars on them.
One thing you should not discount, however, is the Ghost. Trust me on this.