^ if you are using bkf for whitening the mesh on the xi's be careful. It does work and works great but it comes with a downside. The mesh on my og Concords have more of a ruff feel to them than before. I've used the rit whitener to help remedy this feel, but it's not the same. If you have some beaters with a similar feel or texture to the mesh, I suggest trying the bkf on them first. If your satisfied with how they come out results wise, then do it. Hope this helps anyone contemplating doing either procedure.