I have the small and medium sized versions of the S2. While I like the general quality and execution of this model, you should be aware that there is an inate design flaw which predisposes to inadvertant closure during vigorous use. The non-lock side of the frame has a cutout intended to make it easier to close the knife. Unfortunately it is located exactly where the index finger rests when gripping the knife. I'm not sure, but I think the curved shape of the handle may magnify the pressure one places on this location. The adjacent area of the lock side of the frame has no cutout and is scalloped to make it grippier when closing with one's thumb. In any case, all of the above combine to make it unusually easy to release the lock with one's index finger when gripping the S2 tightly. This seems to be particularly true for me if I put thumb pressure on the thumb ramp. Try it on yours to see if you find this to be true.
I did not really notice this fault until another forumite posted that he had been bitten by his S2, causing me to evaluate mine carefully. CRKT initially made this line in 3 sizes, but the largest size was quickly withdrawn from the market. My retrospective conjecture is that the largest size was the one where accidental closure was most likely to occur.
I have several other framelocks and have not seen this problem on any of them (including a CRKT Ti Mirage framelock), although as has often been said: any lock can fail. I think it is the combination of factors listed above that is the isssue with the S2. My Buck Mayo also has a cutout on the non-lock side of the frame, as does my Lochsa. In the case of the 172, however, the index finger tends to rest forward of this spot when holding the knife, and the adjacent lock side of the frame also has a cutout (perhaps a cousin of the Boye dent) instead of grippy scallops. The corresponding spot on the Lochsa's frame has been machined smooth, providing less grip from a thumb pad when purposely closing, but also reducing the chance of accidental closure. I initially wondered why Scott Cook smoothed that area, and this is the only conclusion I could come to. My other framelocks have one or two of the predisposing features I noted about the S2, but each seems to have some design feature to offset the tendancy to inadvertantly close. It's quite interesting to look at all the little decisions that go into designing a really good folder.
I still carry and use my S2's, particularly the small one, which is a nice little Gent's folder. I don't forsee accidental closure while wrestling with a newspaper coupon or attacking an envelope. Hope you use yours in good health; just be aware of a need for caution.