The shape of the hammers are the same, but on a firearm with rebounding hammers after being fired the hammers bounce back off the firing pins to half cock, under power of the main spring, and allow you to open the gun with nothing else needing to be done. On non rebounding guns you need to manually put the hammers back at half cock before you can open the gun. Rebounding guns are just that little bit faster to use.
It was considered that big of an improvement that many guns built before the invention on the rebounding lock had the locks converted to rebounding at a later date.