lol, I'm just keeping my little secret for the time being, I'll give you a clue, the vendor is in high town and the item is in my bag in my screenshot.
If you are going rogue, for a play through for me it was the easiest class to work. The only fight that was truly challenging was the rock wraith at the end of the deep roads expedition. Just work on upping your crit rates as the base damage from rogues is not very high they just have a very high attack speed. I think when I finished my crit rate was around 80% though.