I understand that some knife designers feel compelled to include more safety features, but I personally carry a knife every day, and none of my assisted-opening knives has ever opened accidentally in my pocket. Likewise, I've never been in a situation where a knife's primary locking mechanism (liner, frame, etc.) failed and would have depended on a secondary lock to stay in place. In fact, the only folding knife that has ever "broken" on me so far was a Smith & Wesson Extreme Ops folder that fell apart right at the pivot, where a secondary lock would not have helped.
I'm sure that there are some people who might benefit from such a feature, but the pictured lock design looks poorly located. Yes, it prevents the flipper from moving far enough to engage unexpectedly, but it would be more intuitive to place it where it could be activated either by the thumb or index finger, possibly set into the scale or liner. The CRKT "LAWKS" system, for example, is pretty unobtrusive when opening or closing a knife, but is located for easy access as part of the knife's normal operation.
