I have it in some other Wengers, once open the screwdriver blade slides back a little bit when you put pressure on it (when you press on the screw to drive it in) and locks up to prevent it from closing. When you stop putting pressure on the screw the blade slides back out a bit and unlocks, I don´t know what the mechanism is to do it but it works, I should add that I´ve used Victorinox screwdriver blades a lot and never thought they needed a lock.
Some people prefer the Wenger scissors over Victorinox, basically because of the way the spring works and because they are toothed, I think the Wenger pliers are a bit more versatile that Victorinox because they are slip joint. In general most people still prefer Victorinox.
Personally I have used both and feel fine with either one. I do not consider the difference in scissors, pliers or screwdriver blade important enough to affect my decision as to which one to buy.