I’ve been using it for a while now and find it very useful - it’s my main document library. I paid full price - it’s a real bargain on Bundle Hunt. The developer is very responsive on the EagleFiler forum.
I use just one library, but my work and life tend to flow into each other, so your mileage may vary.
I save quite a bit of web content to the library and find the bookmarklets handy (EagleFiler Bookmarklets). This allows me to choose whether I want to save as a PDF, plain text or as a bookmark. There is quick capture available too.
I store my library on iCloud, so I can access the files there (even though EagleFiler isn’t available for iOS - it’s not really necessary). Flagging an item in EF comes across in Finder (tag: flagged)… I use that to highlight PDF files I want to read later/annotate on my iPad.
You can print a PDF to Eaglefiler from pretty much any application.
You can save emails to the library using the capture key or by dragging from Apple Mail into the library. Indeed, you can add any file to the library by clicking the file in Finder and pressing the capture key.
EagleFiler plays nicely with the Skim (free!) PDF reader - if you search for a PDF and then click on it you’ll be taken to all references of your search within Skim. Apparently it also searches Skim notes.
This feature list is a good summary: EagleFiler Feature List
The manual is comprehensive: EagleFiler Manual
For more advanced usage, including things like OCR, there are a bunch of AppleScripts: EagleFiler AppleScripts.
There are also some ‘esoteric’ settings. EagleFiler Manual: Esoteric Preferences. I’ve found it useful to change some of these - e.g., exactly how a PDF is captured to the library. Might be something for later, once you start to explore the features, but they’re worth knowing about.
Feel free to come back with any questions! I’ve also made some tweaks to better display Markdown files.