Thanks for the feedback. The price information is this:
"Neo-6" from retailer 1 < $3.00 Two modules, both modules completely dead.
"Neo-M8N" from retailer 2 $7.99 No power supplied to active antenna.
"Neo-6" from retailer 2 $4.70 Works perfectly.
Of course, retailers like Adafruit are very reliable. However, up until now, with Aliexpress/Ebay, I have almost always received something at least usable. These GPS modules are a big exception. With retailers who specialize in electronic components, there is an expectation that they can at least test their products. If the retailer is also selling womens' underwear and garden tools etc., of course there are no such expectations.
A clock is not very demanding. The only working module I have picked up a time within a couple of minutes, even with the module on my desk. I think for that only one satellite is required. A full position fix (2D/3D) is more demanding