A thought:
Peter Stuge wrote:
and our product always included the full license and source on microSD, that would not be good enough to cover the obligations of our distributor/customer?
As long as your customer passes the medium along to *their* customer, I would consider them compliant. They have to actually do that however.
It is helpful to state that they are non-compliant and risk a lawsuit should they fail to accompany the object code (in your hardware, which they ship) with the source code that they can acquire or have received from you.
If you can handle the cost then you could design a (read-only, e.g. USB- attached flash memory appearing as a CD-ROM) medium *into* your hardware, which stores the source code corresponding to the object code which is in boot flash. I find that ideal.
If that medium is in the spirit of the license text "a medium customarily used for software interchange" then I think that is an utmost elegant way to not only ensure your own and your customer's compliance (as long as they do not destroy that medium!) but also compliance for everyone who might re-sell your customer's product, or even your module, should your customer's product at some point be stripped apart and bits of it sold e.g. as spare parts.
I think that's a truly valuable offer for you to propose. GPL compliance built-in, so to speak. :)
//Peter