How about a +1 bonus to Strength checks for these circumstances instead. While I can't be certain, your wording might invite abuse of loopholes.
Iron Grip [General]
It's for those instances you can't forsee. Sometimes rules can have a weird synergy that just ungodly.
I believe the DMG talks about why bonuses/penalties are in multiples of 2.
A +2 bonus to Strength is effectively the same as a +1 bonus to Strength Checks as for every two Ability Points gained, the corresponding modifier increases by one. However, since ability requirements for feats are based on odd numbered ability scores, your feat as written could have some unforseen effects. While I can't think off hand of anything that might allow a character to gain a feat temporarily if requirements are met, that doesn't mean there aren't any. I fully admit that I don't know of every single d20 rule/ability/item that has ever been created (by WotC or otherwise); I don't know how two little things might react with each other. Do you? Should I bow down before your supreme knowledge and understanding of all things d20?
How so? The first sentence points out that this feat's used to make checks to maintain possession.