Anyone know anything about disc brakes?

Isn’t there a risk something as hard as that will damage the inside of the frame?

No, none at all - it's tiny. The diameter of the centre section is less than the diameter of the hoses attached to each end, and only a few mm long, so there's no realistic way it's going to hit any part of the inside of the frame. Due to its diminutive size it's a right PITA to install and remove, and annoyingly easy to misplace, but it works really rather well.