Convex Bowl: Other than better stiffness, it is 100% lid-seal guaranteed. If lid-sealing failed due to human error, a second sealing can be applied. The large contact area for sealable film enables the food contained to be safer and lasts longer.
Concave Bowl: the flattened cup rim is folded down, providing better rigidity, stability, and security when using a lid, in addition to all the benefits of a convex bowl.