Very handy, although hard to navigate.

A great addition...when it works. Sometimes it shows multi-library service such as Colorado's Prospector as having nothing available, but when I check further it is available. But overall, this is a super service...sorry, Amazon!

Useful extension. Although the "Internet archive open library" link more times than not, even thought it says there's a copy, there isn't.

A great add-on that could be even greater if the library definitions one selects would also imply their inter-library loan systems. Colorado libraries use a system called "Prospector" that rummages through other systems in the state including university libraries, etc. If the Extension library definitions could somehow pull in the inter-library systems as well, that would make a great add-on even better! I'm pushing my luck here, but since there's an exhaustible list of libraries to choose from in the extension, perhaps a "nearest availability" option where, when a book isn't available from the chosen list then the next best/nearest availability option could be shown?