"When the item is free, you are the product" is the lesson of this past decade. I am at least repeatedly learning this over and over again.
[0]: http://www.microsoftstore.com/store/msusa/en_US/pdp/Windows-...
"Free" in that context is what I am referring to.
A more accurate lesson would be, "if the item is free, and often if it is not, you are paying for it in something other than money, or are receiving benefits incidentally to someone else paying for it."
Win 10 isn't free.
That's at least my way of looking at it.
That doesn't make the software's user "the product" though. In your case the developer is making himself the product he tries to sell, not the users. This is really not comparable to advertisement and data collection.
Telling people not to trust anything they don't have to pay for seems a really obvious footgun for FOSS.