1. The first difference is purely cosmetic; the Milspec Plates have a matte black finish, vs a glossy black finish on Black Bumper plates. Milspec plates are also slightly thinner than our standard black plates, with a more rounded edge. In the end, both plates are great, and you should be confidant in knowing you are using the best bumper plates on the market today.
2.The second would be the center inserts. The Milspecs has a regular steel insert and the Black Bumper have a "hooked' steel insert. The hooked design distributes stress more evenly across the plate, which helps prevent cracking, chipping, or deformation of the rubber coating. Hooked steel inserts often produce less noise and vibration when dropped compared to plates with regular circular inserts. The secure connection between the hook and the rubber dampens the impact and reduces the rattling or clanging noise associated with weightlifting movements. Due to the center inserts we recommend gym owners get the Black Bumper plates! Longer durability!
3.www.garagegymreviews.com/best-bumper-plates-guide. Great guide by Coop, Garage Gym Reviews.