The reprint has changed Enhanced Vitality, but now rather than merely pretty bad, it seems almost entirely worthless.
Now, using Con to make saves against what would normally require a mental stat save would be a huge boon for the Berserker, who is likely to have dumped at least one mental stat. However it's limited to effects that deal half damage on success. And my first thought is, are there even any such spells?
Doing a search of the spells in the PDF, I only found two spells (one Int, one Wis) that have a mental stat save that halves damage. Since you can only pick one stat for this to work with, it seems like this feature allows you to choose one single spell that you can roll a Con save on to reduce damage, instead of Int or Wis (there are no Cha options).
I also started searching the monster manual to see if this is useful on some non-spell abilities, but so far am not finding anything different than the usual spell expectations, where mental saves are almost always for status effects, and for the few that do damage, it's all or nothing, not save for half.
Am I missing something? This seems beyond horrible, particularly compared to Preternatural Evasion.