tl;dr (too long, didn’t read)
Cr-Mo is a heat-hardened steel alloy, with the inclusion of molybdenum that gives the alloy a property of toughness and flexibility. Cr-Mo will absorb percussive impact better than Cr-V without being brittle. Over time Cr-Mo sockets may stretch and lose their shape, but they are less likely to shatter and cause injury.
Cr-V is a also a heat-hardened steel alloy that doesn’t have the same properties of flexibility and toughness under impact load. This means that Cr-V sockets under impact can be brittle, and prone to shattering, endangering the user.
Check out our 10mm to 32 mm CR-MO impact set with foam organizer tray.