CRAFTMEMORE 3/4 inch Metal Curved Side Release Buckle Clip Lock for Belt Paracord Bracelet Pet Collar 2 pack

Can this be used to replace existing buckles? Do they come apart to attach to existing backpack belts (closed loops)?

Is the gunmetal buckle painted? Is the black buckle painted? I see a review mentioning peeling paint on the black color. Also, is either color shiny?

How much weight can this buckle hold before it pops open? (I'm looking to replace the plastic buckle on my 30-40lb backpack.) Thanks!