Can open on many carabiners
I recently bought this knife because of the claim on Trango's website that it was impossible to open when looped onto a carabiner. Turns out this isn't true. I managed to open the knife on every carabiner I tried (a Petzl Williams screw-lock, Petzl Williams triact-lock , Petzl Attache screw-lock, and Black Diamond positron screw-lock). It's true the knife won't open on the main body of the carabiner, but I was able to open the knife at the point where the carabiner thins at the top of the gate (even when the carabiner was locked). Since I was only able to open the knife on one small portion of the carabiner, I imagine you'd need to be pretty unlucky to have the knife open up on your harness, but it's definitely possible. Also, in the knife does come open, keep in mind the tip will likely be pointing up towards your torso where it would be easy to cut your arm on the knife. With a different knife (like the Gerber Remix) if the blade comes open, it will be pointing down towards your leg where it seems less likely to cause damage to you.
If the knife was truly impossible to open on a carabiner, I would have given this five stars, because everything else about it is pretty awesome.