> There is a huge price spread on nearly-identical products because people don't have enough information to determine which of the various supposedly equivalent products available are more reliable, efficient, safe, etc. and this is reflected in people spending more than necessary.
Information about a product is part of the whole package. It's ok that people pay extra for it.
You even get effects like what you describe in some of the most efficient markets. Eg aluminum that's traded on the exchanges often sells for a different price than over-the-counter deals. See https://www.bloomberg.com/opinion/articles/2014-11-20/the-go...
That doesn't mean that the market for aluminum is not 'efficient'. It's just a bit weirder than a naive look at the physical properties of the ostensible good, aluminum, would let you to believe.
Basically your critique says 'there's this subset of physical properties that is the same for two products, but they sell for different prices; hence the market must be inefficient'. But products aren't always made up of their physical properties alone.
Eg suppose I have a business selling sheets of paper with the winning lottery numbers of five years in the future. This is a product with a lot of information asymmetry: you can only judge its quality five years after buying it. To make it more extreme, assume that my predictive powers aren't quite so awesome: I can't divine guaranteed winners, I merely manage to produce lottery numbers that are a thousand times more likely to win than your average number. Still a useful product, but even harder to judge by individual customers.
Now a competitor springs up who sells the same sheets of paper with numbers printed on them. It's just that my competitor's numbers are no better than chance.
The physical properties of the paper and ink are exactly the same. They even use the same font. A lab couldn't tell them apart.
Would you insist that both suppliers' products should sell for the same price?
Now assume that I don't even print my own sheets: I just buy them in bulk from the other supplier, but I only resell the sheets that have the increased chances.
Now the sheets really are identical, and the only difference is my reputation for quality.
I hold that an efficient market will have different prices for this ostensibly identical goods.
> If, in fact, a particular brand was consistently more reliable than others but priced at a premium then with perfect information everyone would know this and a new manufacturer could introduce a similarly-reliable product at a price point within the spread and everyone would buy that instead.
Yes, that strategy is available even with imperfect information. And we often see that in the market, see https://scifi.stackexchange.com/questions/184207/was-the-jok... for an example from popular culture.