All the above are "correct" ways of using Opti-Seal. Opti-Seal has many uses in detailing and due to Optimum's synergy can be combined with other Optimum products with success. Will mixing it with ONR, or using it as a drying aid shorten it's life expectancy in terms of protection, yes it will, that said it will speed up the wash process and give a superior result that you will want to use it every time you wash.
Opti-Seal also makes a great glass cleaner, put it on dry glass with the included sponge(sparingly, but everywhere, and dry it off with a MF towel before it flashes completely.
You can also use Opti-Seal as an interior dressing that leaves a nice sheen without being greasy, and it's anti static.
Of course as a sealant that you apply to freshly polished paint Opti-Seal excels, and in this manner you will get the longest durability.
As a drying aid with ONR, wash with ONR, and sparingly spritz Opti-Seal on the panel, then starting where you sprayed, dry the panel.
Another use is as a protective layer over Opti-Coat Pro or Gloss-Coat as they are curing. 1 Hour after the coating is applied, apply Opti-Seal to the coating, this will allow you to release it to the customer in safety regardless of the weather conditions as the Opti-Seal will protect the coating in it's critical first week.