The unfortunate things about clones is they have such effective counters. Place a single Kylo Ren (probably not even need to be zeta'ed, but definitely 7* gear 11) and let Cody's 212th attack loose on him and you may be hurting by the time of Kylo's next attack.
As has been said, maybe they're effective above the top 100 in the arena, but at some point below that they start to fall apart.
In GW, however, with a zeta'ed Cody, they're amazing. I used them on nodes 1 - 5, sometimes 6, 7, 8, 10, and broken 11 and 12. They stay with full health and protection through most of it.