Leakage is hard to measure by consumers as it must be measured by somebody else while you are listening and they don't know what volume/genre you really are playing (and if it is well above safe volume levels that cause you to go deaf instantly). I will tell you this, when my teammates and I test M-100, I have never hear anything they are listening to ever ever ever, even sitting next to them. But I think I listen a bit louder, so I always wonder if they can hear me because I tend to listen louder and to EDM vs classical/jazz/acoustic. I can tell you that every person I've ever seen listening to Crossfade LP, LP2, M-80, M-100 so far I haven't heard anything but the faintest sound that I can remember.
However, I'll try to get more scientific in this area in the future but we rarely had a complaint on LP, LP2, M-80 and they are fundamentally the same so I strongly feel that we have the right balance of soundstage, isolation, fit and leakage (which are all interrelated).