Please don't respond with inaccurate answers to questions like this if you don't know the correct answer. It is extremely damaging to others when you spread misinformation.
FlexMed is not binding at any point in time. If you are accepted, you do not have say yes (though the yield was voluntarily 100% last cycle). Even if you accept, though you cannot apply to any other med schools or take the MCAT while you're still in program, there is no binding commitment to attend med school. You can back out of the program should you realize you'd rather do something other than med school. The entire point is to allow exploration of other areas, so they will not force you to attend med school 2-3 years after you've gotten in FlexMed. Hypothetically, you could even get accepted, say yes, back out of the program if you don't like Sinai anymore, do regular apps, and get into another med school of your choice, but that would be morally reprehensible.
Source: actual interview day experience.