It seems hard to use to be honest, but I have to buy it anyway and I do so loathe to waste things.
- 30 minutes to perform the ritual, so unless it's a prepared fight then it's zero use in combat.
- It stays just one hour for each success, so even a planned combat is difficult to make happen, unless you can spend 30 minutes within a reasonable distance of the combat, or roll really well which cannot be relied upon.
- After you summon it, you still have to persuade the spirit to actually use it's cool powers to assist in your request.
The most interesting uses seem to be non-combat, with Bone Spirit or Fog Ghost being the combat spirits? Spellcasting seems interesting, as Ally spirits can gain access to any spell it seems, up to a rating equal to their strength, so if you need a specific spell it's no farther away than 30 minutes and a few good rolls.
THAT seems powerful, but is subject to DM-approval as "
The gamemaster should determine the exact powers and spells of a particular ally spirit to suit the nature of the spirit and the needs of his game." - p. 376 of GMG.
The same can be said for talents. Need a magically trapped door opened and there's no rush, then summon yourself a buddy with rank = strength rating in Disarm Traps and Lock Picking.
