You can apply a cleaner wax over sfx-3 (I've done it). Cleaner waxes are more of a go between before a pure wax or as a one-step product if you do not have the time to properly prep and seal your car.
I have found Mother's cleaner wax to have been especially good. I like to use the cleaner wax right after a final polish, and then add my wax lsp.
I also have used extensively Sonus' SFX system. I prefer (even though you can use a cleaner wax over it) to use an acrylic glanz right after the polish. The glanz will provide an ultra thin coating that will smoothen out any left-over haze from the polish, and will add a hint of gloss to the polish finish. After the Glanz, then I would top off with my favorite lsp.
IMO cleaner waxes are not nearly as good as an lsp as compared with either a synthetic lsp (sealant) or a pure carnauba wax, but it can work well with a carnauba based lsp in providing the final finish.