I have the M16-14SFA, and at the time I bought it the M16-14SF was not available. The SF was a few dollars more, why....I don't know because the specs appeared to be identical. As previously mentioned, for about $50.00 it's a decent investment.
And, and I have never had a liner lock failure with my CRKT's, and I have about 12 of them, M16's & M21's. I'm not one of those who look for liner failures by throwing at walls, chopping trees, prying paint cans, puncturing car doors, or whatever in a absurd use of a folder. Abuse ANYTHING, and it will fail you.