Neither are really necessary under Rex lead, but the unique is certainly useful. The Furious Foe special zeta is usually not very useful, but I did it purely for completeness (and may have also been drinking). It has actually come in handy a few times in arena against RJT's protection gain, if it's well timed and EP isn't dead yet it can stop him from healing back to full health. It makes dropping Vader faster at the end of a match as he won't be healing from EP's lead (or the DOTs expiring if he's got his zeta unique).