This really seems like a card destined to be used mostly by off-mystic subclasses. Most purple characters don't really want to testing non-will stats even if they get base 4 for free, and they have other things to do with their arcane slots. Maybe a full-cluever purple runs eyes/daemonic/wings with St. Hubert's Key and Ikiaq alongside their Clairvoyance to imitate Pathfinder Ursula Downs, or maybe when Marie Lambeau or Amina Zidane go to Dunwich they run Daemonic/claws to go hunting Whippoorwills and Acolytes, perhaps running Blood Pact to test at a cozy 7. But it's a really convoluted way to do stuff mystics can mostly already do.
On the other hand, 4 XP is enough to get Dominance (remove ally slot), Wings (you can move with it), and your choice of the fight/evade/investigate options. That's within reach for all the 0-2 mystic types, who can run it as an arcane slot passive that gives them a free move or basic action most turns instead.
Patrice Hathaway is especially well-positioned to take advantage here. She has 2s in all non-will stats, so the base 4 is always a +2. Despite Will being her best value, she can't use big mystic spells for her action compression. If she runs this with Foolishness, she can now replace her base stats twice per turn. And with 5 draws a turn from the survivor pool she can easily access enough commits and boosts to make the servitor succeed or just use it to trigger failure cards. Her biggest problem is a shortage of actions, though, so you may want to include some fast assets like Fire Axe, Plucky, or Talisman of Protection as Servitor food.
Daisy Walker actually loses book if she makes it investigate for her, but a free investigate at -1 is still good, and leaving it behind in a hazardous location is great. It still benefits from Magnifying Glass, Dr. Milan Christopher, Death • XIII, and so on. Alternatively, she could take it on evade mode. It would test at 5 with Hiking Boots, 10 with Mind over Matter, and if she Transmogrifys an enemy she can still snag clues with the evade servitor.
Sister Mary can take it to supplement her damage or clue output, since both are base 3, and then boost them with Ace of Swords, Beat Cop, St. Hubert's Key, Field Agent, and so on. Honorable mention to Alice Luxley who apparently loves getting tips from beyond the veil, since the servitor gives you a safe Investigate action to trigger her damage with when engaged by enemies.
It's a little more awkward for the event-focused Sefina Rousseau, and because it's not really an ally Charlie Kane can't take it unless he commits to the mystic class. But it's potentially interesting if he does, despite being grossly outshined by Summoned Hound cheese if you play that way.