No, I think you've got it right, though I don't think it's quite correct to say it's for people who don't know that it's already available for the free ereaders. Your mom has you to figure this stuff out for her (I'm assuming); for those of us who have to figure it out for ourselves and who aren't technical, there's a tradeoff between time and cost. I was happy to pay the $2.99 to not have to spend any time on this since it took me long enough to figure out how to get the Calibre file type plug-ins working and then to set up my Kindle to access the Calibre server so I don't have to sideload. I know those are simple things, but not for me
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The only thing that gives me a bit of a qualm is that I don't know whether it's considered that the fellow who made the app is profiting from all the hard work that Kovid and others have put into Calibre. I wouldn't want to be part of that, but I haven't seen anyone suggesting that yet.
Sorry it took me so long to respond to your previous post!