I picked one of these up in a trade recently and here's my initial impressions compared to my Tenacious:
-Noticeably heavier
-Opening the knife isn't as easy. As other members have already described when opening the Vex the hole goes too close to the handle. The Tenacious is superior in this respect
-Tip down only (Right or left hand though)
-Ergos are good except the corner on the top rear end of the handle is uncomfortable. The design of the Tenacious also puts the blade at a better angle
-Blade is nice and thin. Good geometry, though the edge bevel is a bit obtuse like pretty much every factory knife
-Opening is smooth, lock feels solid with no play, good F&F in general
It's a good knife but I see no reason so far to buy one over a Tenacious unless you feel the ergos and blade shape work better for you. The latter has 4 way clip mounting, better ergos, is lighter, is easier to open and close and isn't as thick as the Vex.