Ardenas Barehand:
Magic, p. 19. If an item has any "mage only" effects on it, only a mage may use the item's powers. (emphasis original)
I have no idea what this "Stack Exchange" is, or what the answer you got was (I always recommend the GURPS forums at
http://forums.sjgames.com/ , as you can get the Line Editor and book authors to answer questions there), but...
The answer is: "Mage Only" is a descriptor in the "Item" section of a spell's description. If it says "Usable only by mages" then only mages can cast the spell using the item, there are no other prerequisites (so if it's "mage only" all you need is Magery 0).
Frex:
Lend Energy
Regular
Restores the subject’s lost Fatigue Points, at an energy cost to the caster. Cannot increase the subject’s FP score above its normal maximum.
Cost: Any amount; the energy spent by the caster goes to the subject as restored FP (e.g., if the caster spends 5 energy, the subject regains 5 lost FP).
Casting cost is not reduced by high skill.
Prerequisite: Magery 1 or Empathy (p. B51).
Item
Wand, staff, or jewelry.
Energy cost to create: 100.
Regeneration (VH)
Regular
Regrow one lost limb or eye.
Duration: Permanent.
Cost: 20. One try.
Time to cast: 1 minute to cast the spell; 1 month before the process of regeneration is complete. The regenerating part may not be used at all until the month has passed.
Prerequisites: Magery 2 and Restoration.
Item
Wand or staff, decorated in a snake pattern.
Usable only by mages. The item must touch the subject.
Energy cost to create: 3,000.
(Goldenrodding mine for emphasis)
In this case, a wand, staff, or piece of jewelry of Lend Energy is usable by anyone, but a wand or staff of Regeneration is usable only by mages (and since Mages don't generally get Regeneration in DF, this should be "usable on by Clerics/Holy Warriors").
gwythaint,
Since you're using the Magic Item rules from DFRPG Magic Items, and this has literally never come up before (even on the sjgames forums*) what effect will Magic Resistance have on casting spells from items or scrolls? If Power Talents add to the casting, I'd recommend that Magic Resistance actually penalize the casting. But those are my two cents (as probably the only Player with a Character with Magic Resistance...).
* I started a thread:
http://forums.sjgames.com/show...=2283846#post2283846
This message was last edited by the player at 02:18, Mon 09 Sept 2019.