Re: DND 4E: Temporary Hitpoints question
I agree with elecgraystone, and Syrris' interpretation about rules-as-intended.
Keep in mind the premises of the item:
This is a shield, so used primarily by Defenders and Leaders. The PC using it has chosen to use their Arms slot item for something to help their friends, not themselves.
This is a level 15 Uncommon item. There are other alternative items with impressive abilities.
The number of Temp HP we're talking here is pretty small for level 15+, short of certain synergy you might get if the Leaders in your party have strong Temp HP powers. A bonus of +3 is further pretty small regardless of how many THP the theoretical power provides. Keep in mind your fighter at level 15 would have at least 99 real HP.
Whatever action is being used to grant the user of the shield those THP, is an action that in most cases might have otherwise been spent on doing something beneficial for that ally in the first place. Economy of actions. Your power that gives you 5 THP let's say is a Minor action -- you could have had a minor action power that gave a direct boost to that ally's defenses instead, or some kind of attack booster, etc.
The ally must be adjacent, which is typically either dangerous in itself (presuming at least one of you is engaged with an enemy) or at the very least somewhat inconvenient.
Under normal intended uses, I can't see the most liberal interpretation being a problem to the game.
As a Battlerager however, there becomes the game issue of making yourself into something of an off-leader, effectively throwing bubbles of THP all around with Free actions, as you yourself gain THP as essentially free actions with Invigorating powers plus however many other THP-related things you do. You could further push the envelope if you had optimized your character to be an unending source of massive THP.
I would advise a GM concerned about that to consider the numbers actually being involved, and whether it is really a bad thing for the game in question. And if they were still unhappy with the prospects, it's easy to houserule that the shield's property only works either once per round, or only when the THP received are from an outside source, or something of the sort.