Went with a helm because there was a helm gap in the available sets in that area. Could have gone Gloves or Boots but Helms can look REALLY cool.
You're not thinking like a player, Grim. The vast majority of epic use is for stam gain, so it doesn't matter what sets it complements.
When thinking of an item slot for a new high-level stam gain epic, I would suggest looking at the highest level stam gain item for each slot, and releasing a high-level item for the lowest of those numbers. Right now, the highest level stam gain epic for each slot is:
Gloves: Vine Tendril Gauntlets, lv 1200
Helm: Mask of Terror, lv 1600
Amulet: Choker of Time, lv 1925
Weapon: Krakaradon Tooth Harpoon, lv 1200
Armor: Dragon Draped Breastplate, lv 1101
Shield: Elemental Shields, lv 900
Ring: Nutcrackers Walnut Ring, lv 900
Boots: Dragon Draped Sabatons, lv 1101
Rune: Roach Rune of Epidemicus, lv 1200
Since the lowest number on that list is 900, the newest epics should take those slots. That would be either a shield or ring. Special mention to gloves because that's the only one of those that isn't a titan item. Aside: I would love to see high-level epics that aren't titan items, especially if they become the best available in their slot.
Amulet would have been the worst choice but helm was not far behind. Having the Mask of Terror be a helm was the worst slot to use for that one.
As for the artwork, it is a problem to illustrate a horrifying monster with a really wicked-looking ring or rune, I understand. Still, I don't believe it's a big enough issue to overcome everything else.
One fix would be to keep the current helm as is and introduce a recipe to transform it into a shield. The shield on that artwork looks pretty nice too. This would be similar to Dragonbane, where you put the item as an armor even though there was a glaring hole with boots (and we already had a +3 stam gain Ridged Legion Breastplate).
If you don't like the effect that has on the market, put a special flag on this new item that doesn't allow it to be saved with Inventor II, or instead of having a recipe for it, make a "swap shop" in the Cathedral of Ways where you can trade in one for the other.