Many, if not all, guides recommend this on him. But if you read the fine print on it, it will only be half as effective on Thresh due to him unfortunately counting as ranged (which is why 
is so tricky to use with him).
Are they not reading the fine print, or would you consider Knight's Vow worth it even if only half as effective as on, let's say, Braum or Leona?
agbudar2 votesany less damage taken on an adc is good.
its not just that though
you get a whopping
60 armor
400 health if you are near your target thats a lot.
that being said i think 
is the better item since it can cover bad adc much better and good adc will make that much better use from the shield anyway.
Bootleg Gay1 votesI wouldn't get it. I'd invest in 
and 
instead. Thresh is a strange champion in terms of build paths, since he is both ranged and tanky.
Tormentula1 votesIt can work on anything honestly, I'd build it for the armor since it's pretty cheap. I've even seen both new items built on thresh cause, why not really.
Oglaf1 votesI've been rushing lately (even before Sightstone, lulz) and I find that the offensive punch it offers is amazing; especially since him being ranged to poke the enemy finally works out in his favour for once!