This reviewer is apparently reporting several problems:
1. Gas mileage goes down in winter.
Boo hoo. All of us living in a cold climate experience it. There's nothing wrong with his car. His reported "low" mileage is better than mine during this Wisconsin winter. He shrugged off his tech's attempt to explain it, so there's nothing more I can add. Those of us in these forums believe we have explained it thoroughly, and we just live with it and wait for the spring thaw. (It doesn't have anything to do with oxygenated gas or a delicate engine. I doubt his tech told him that--more likely he was confusing several things the tech said.)
2. The fuel gauge does funny stuff.
Yes. We have investigated it and concluded there are unfortunate side-effects of the fuel tank design, which was intended to reduce emissions. Fill up your tank before it drops below 25% if you want to be safe.
3. The stereo was blasting static.
Sounds like a defective stereo--that should be a quick fix. There have not been many similar problem reports, so I doubt this is a widespread issue.
4. Check engine light
He didn't tell us what engine code was logged, but his subsequent comments indicate the tech thought the engine was misfiring from watery gas. Switching gas stations and keeping your tank at least 25% full are good solutions to this problem. Again, lack of similar problem reports indicates this is not a general Prius issue.