I've been wanting to find a reason to slap this on an Oldblood or Scar Vet as a normal kit-out but am struggling to find a real reason why you would take it over something like AoD. It's pretty easy to get a 1+ with this, but anything that can wound you twice probably is a high enough strength that your amour doesn't matter. The only real time that I've put this to good use has been against WE waywatchers, in which case it really shines. Besides that (low strength, ignore amour shots) I haven't been able to think of a time when a normal 1+ and/or a ward wouldn't do the same job for cheaper. I've never played against anyone who has taken it either. Has anyone figure out a good utility for this and are there other races that can make better use of it, or is it mostly and overpriced gimmick?
It's a bit overpriced, but I wouldn't call it a gimmick. I have yet to use it as my closest circle of competitors tends to play high Strength armies like Dwarves and Chaos, but I wouldn't mind using the Helm if I fought Elves (well not High Elves), Empire, Brettonians, Skaven, and other armies that have a relative dearth of Strength 5 or 6 attacks. The Armor of Destiny will stop half the incoming attacks with it's ward save and provides heavy armor which we have limited options to get. The Trickster's Helm will half your damage by things Strength 5, do a little better than half your damage for things below Strength 5 and worse for things above Strength 5 (and nothing for things that don't roll to wound) and you would need to buy light armor to equal the armor save (or be an Oldblood for the better Scaly Skin). The nice thing about Old Ones is you can shell out the points for the Trickster's Helm and still pack a Ward Save with a second item (or some other item). A Scar Veteran is stuck with the one Helmet. If I go an Oldblood and Scar Veteran, the Scar Veteran nearly always gets the Armor of Destiny and then I mix it up with the Oldblood. Usually Glittering Scales + a Talisman + a cheap weapon. I can see giving and OB the Trickster's Helm.
Often playing Skaven, Undead and elves, I love Trickster helm. My usual setup is 1 oldblood, 1 scar vet, and I often use the AoD on the scarvet, and Trickster helm + Talisman of Preservation on the oldblood. Get off even a simple Wyssan makes him a hillariously tough nut to crack, or if I place him in a unit with a life slann... Of course, it's useless against poison and Runefangs, but it's EXTREMELY useful against killing blow - it's very rare to get struck by a killing blow when using trickster helm in my experience, and killing blow especially sucks because it negates your armour, making that +1 armour useless anyway.