The convex cups force you to play efficiently. You cannot produce a sound if your lips collapse into the ‘cup.’ I hate standard bowl shape cups. Stork makes a great piece, the VM6. V in shape and incredibly efficient. The Warburton SV design is also very good.
I would be playing a convex cup now if my budget allowed it. I find them to be incredibly versatile. Legends makes a few different types and I hear Derek makes great pieces.