Thanks, everyone. I truly appreciate your feedback. I'd sort of worked out that Kindle was a dispensing device for Amazon's ebooks, much as cheap inkjet printers are sold at cost-plus and the manufacturers make their profit on the consumables.
Problem is, if Kindle gets a lock on the market, it becomes a one-channel solution. Whatever color you want, provided it's black?
But thanks to your good advice, I've already downloaded Calibre. Thanks, everyone.