Again I will raise the issue on Masterful Shank. We have a few of them rotting in banks now. I am hoping that with the change of vizel going offhand, a change of the mind on masterful shank can happen.
Currently it's too weak to be a rogue main hand weapon for backstabbing. A ranger and rogue, if they don't have vizel and are raiding CoM... which is a low chance. Would use vizel in main over this. Even if they didn't have a vizel, all the other 1h weapons from CoM, are mainhand/offhandable. So the axe, karnors sword, the bard only weapon etc. Beast if they didn't have a vizel might use it, but again, likely they'll have a vizel.
I don't think it's overpowered to have it offhandable, and instead just creates options for people who are itemizing and gearing up for a fight. In general, since the vizel becoming an offhandable tower has come down. I essentially think every 1h item should be primary/offhand for the classes that can use it. Weapons only get worse in an offhand. I take a big penalty to put it in a offhand.
In eq originally, there was a case to make weapons OFFHAND only. They'd be quite powerful and too powerful if they went into the main hand. That I can understand, but the other way around doesn't make sense to me.