Thanks everyone. I emailed Prestone and asked this: "Triumph specifies their brand of Hybrid OAT antifreeze for my 2016 Street Twin. Is Prestone 50/50 compatible with this engine, and with the various seals that it comes into contact with?" and the answer from this was: "Yes, it is. Please let me know if you require anything further. Sincerely, Aaron Jones, Prestone Consumer Relations Representative. Phone: 203-731-8191
The description of Zerex G-05 also looks fine. So it will be one or the other depending on what's in stock at the local auto place.