I wonder if Walgreens is complying with GPL by including a notice for source with the device, and some way for customers to access it. Certainly Maylon Group doesn't seem to have anything on their site.
I mean this in a genuinely inquisitive spirit: is it Walgreen's responsibility to provide such a thing, considering they are just the retail outlet for the device?
I would expect that Maylon Group (or whoever is the actual system integrator) is on the hook for publishing customizations.
If Walgreens are distributing (ie selling) a product containing GPL licensed software, my understanding is that they are legally responsible for GPL compliance.
Of course, in practice, it's really the Maylon Group or whoever that will have to provide the source.
However, to the best of my knowledge, the customer's only legal contract is with Walgreens, and its up to Walgreens to deal with Maylon Group (or whoever their supplier is) and ensure compliance - the end customer can't make any claim on Maylon directly.
(Sorry to sound like a broken record.)