Rare Mantis Blades allow you to apply Mantis Blade Edge Mods, Epic Mantis Blade mods allow you to apply two mods - an Edge mod and a Mantis Blade Rotor mod. Other than the price, the differences between the rarity levels for Mantis Blades are which mods you can apply to them.
The Street Cred level you need for each rarity level of Mantis Blades are:
The rarity of the Mantis Blades decides the price, the Street Cred level required to use them and how many mods can be applied. There are three different rarity levels for the Mantis Blades - rare, epic and legendary. Once you've installed the Mantis Blades, you'll be able to use them instead of your typical melee attack to deliver a series of powerful blows to your enemy. Mantis Blades are one of the four Cyberware available for your arms in Cyberpunk 2077 and are an excellent choice for your one Cyberware arm slot.
Mantis Blades and rarity difference in Cyberpunk 2077 explained For more help with Cyberpunk 2077, we have pages on life paths and attributes.