If you buy as a kit you save a little money so I originally bought the kit for an AR and then added the extras I needed for other firearms.
All of my adapters and slings from them have held up to the abuse I put them through (3 gun, personal protection training, coyote hunting).
Here's a link to the first kit I bought, but it comes with a plate that I doubt you need. Really for the most part you are just picking what kit you want.