I dislike these type items for a few reasons.
It messes with organized play, you could find one before the level where you can respec and build your character around it.
Would someone actually do a complete respect based on an item that they very well could lose at any moment? That seems odd to me.
It never goes to the class or character you think it should, the strength gauntlets end up with the priest since the fighter has already spent his ability score increases to get to a 20, all this does is piss off the fighter's player.
Can't say I ever saw this happen in nearly 35 years of gaming. Every case that I can remember, the party decided to give the items to whoever could benefit the most, and no one got pissy about it. If someone did, they probably aren't grown up enough to play at our table anyway.
They don't work for everyone, it is weird that a headband that makes everyone else smarter doesn't make the smart wizard any smarter.
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That's because those items aren't "makes you stronger by X amount" but are "makes you as strong as an ogre." Hence the name of the item. It would be pretty silly to have an item that is called "gauntlets of ogre strength" and the person who puts them on is only as strong as an average human if his or her strength was weak to begin with. Those would be "gauntlets of human strength". If you're already as strong as an ogre, I would expect that an item that it's name implies you get ogre strength wouldn't do much for you.
to the OP, I would have them in a random pile of treasure. Things like monsters, treasure, etc all exist long before the PCs ever decided to explore the area. If someone wants a specific item, I make into a quest. A few years ago, the paladin wanted a holy sword (as paladins are wont to do).
He had to kill one of his arch enemies who wielded Blackrazor. Then take that sword to a lair of a white dragon and have it breath on it. While frozen, he had to smash the blade with Whelm, and then take the shards to the high temple of Cuthbert and have it reforged. So in order to get his holy sword, they had to fight this guy (he was part of the ToEE main plot), then go to White Plume Mountain to get whelm, and then go find a white dragon.
It was a great campaign actually.