Unless someone screwed it up when building it, it's not possible to tell if it is a factory made Del-Ton or if someone built it from one of their rifle kits. The most obvious tip off is the rear sight. If it has to be cranked over to one side then that means the front sight is not lined up properly. Meaning they did not prevent the torquing of the barrel nut from turning the barrel. If the rear sight is in the center and it shoots straight, then it doesn't matter who built it.
As for quality, my son and I have several Del-Ton complete lowers, bought after the first panic and before the current one, when prices were rock bottom due to the glut. All are competently made and totally reliable.