I don't like needing to use sealer, it should really only be used to cover up a problem. The only time a guy trying to do a nice job might need sealer is to provide a uniform ground coat for a poor hiding (transparent) color. Lately what I do in that case is get a solid basecoat color that is similar to the poor hiding color and spray a coat or two of that first. This also seems to help metallic control on the following coats.
So, just say no to sealer. 2K primer is an excellent substrate for topcoating with a very few exceptions.