The drill I call "check swing" is very similar to the "torque" drill. It is one of the most productive drills I use. For one example, batters who don't use their lower half very quickly get past that issue. There are other great benefits, also.
As far as locking the front leg, that should only happen as it would in a normal swing.
Why we are posting video, any chance you have the check swing drill on video?
SL