Don't use either thief AF or this thing...go get a Black cotehardie, JSE body, or scorp harness (if your a buhjillionaire). This is very nice for soloing though.
This is great for a THF while soloing, if you don't have a Scorpion Harness. For PT, Black/Flora Cotehardie is much better (or, again, Scorpion Harness is best). Rogue's Vest is just plain crap, even if it is quite stylish. I only use it for when I'm not fighting anything, simply cuz it's hot on Mithras. XD
I got one of these for myself... cost me 750k. I believe it's worth it, as it is almost as good as the Scorpion Harness for soloing (and I solo a LOT), and the harness is 6 million gil (on Quetzalcoatl). These are quite rare on the AH on Quetzalcoatl; only 1 or 2 go up every month or so. I count myself lucky to have one.