First, you could read the book in the browser. This is a surprisingly good way to go because it turns the e-book into a sort of lovely Web app with sophisticated, thoughtfully arranged controls, including a choice of typefaces, a font-scaling slider, an offline mode and options for creating bookmarks, highlights and notes.
Second, you can hand off the book to Amazon for reading as a Kindle e-book. This makes it available on any Kindle device, within any Kindle app and within a browser via the Kindle Cloud Reader. It will remain in your Kindle library forever, but once the lending period is over, you can't open it unless you buy or re-borrow it.
Either the browser or Kindle option works for me, but I don't use them interchangeably because they can't sync with each other. But if you stick to either browser or Kindle reading, syncing from device to device does work reliably.
There's a third option: Downloading a book to your Mac as either a PDF or an ePub file. These are copy-protected files that use Adobe encryption, so you need to install Adobe's aforementioned Digital Editions app for Mac. If you are also using Cloud Library, you can conveniently consolidate borrowed books from both systems in the Adobe app. But beware: Digital Editions can be unstable and uncooperative about loading e-books.
OverDrive has a selection of native apps for desktop and mobile, but these are optional, do not give you any additional reading options, and do not provide any significant advantages over browser-based access that I can see. In fact, the apps merely pull up my public library's site, browser-style, when it's time to check out a book. I couldn't even install OverDrive's Mac app for the life of me, and I have been trying on multiple Macs for weeks.
Because of e-book borrowing, my e-book purchasing has taken a dive — my last Kindle purchases were in December of 2013. In the months since, I've checked out dozens of books from the St. Paul Public Library, and I'm having the time of my life.
3M Cloud Library and OverDrive are still far from perfect, as I've noted, but their flaws are now modest enough to forgive given how they put a world of books at my fingertips...and the price is certainly right.
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