Possibly some of the best designed Pro apps for the App Store come from Readdle. Documents is outstanding for professionally managing your files and PDFs. Check it out: Documents by Readdle by Readdle Inc. https://itunes.apple.com/us/app/documents-by-readdle/id364901807?mt=8
There is a difference between storing a few dozen pdfs for fun and an academic research collection extending over thousands of PDFs. Academic reference managers can filter and sort by date, authors, subjects, journals, keywords, they can automatically fetch new articles from academic search engines, they handle citations in some word processors via plug ins... Documents by Readdle is a lovely little app but it's not the same thing as an academic professional tool. It's like comparing a home espresso machine with the customizable beasts they have in real coffee shops.
Out if interest: why do you consider some of these apps evil? And why is one the ethical choice?
Because of the companies that acquired them. Mendeley used to be a neat bunch of folks. Same for Papers, they were PhD students in the Netherlands who hated Endnote for its general crappiness and high price. Then they were bought up, all of them, by big publishing giants. Except for Sente, which went bust (or anyway died off) and Zotero, which remains independent to this day.
Mendeley in particular had the misfortune of being acquired by Elsevier, which out of all the giant publishers had the reputation of being the most evil. Among the dirtiest tricks they used to play, is creating a bunch of "fake" (ie. filled with junk, non-peer reviewed) journals, and then forcing university libraries to purchase access to the real, reputable journals only via an expensive bundle with many of those fake journals... (like saying: you need a toothbrush (price: $5), but you can only buy it in a bundle with toothbrushes for cats, dogs and every animal species (price: $5 each) for a total bundle price of $500). Something like that. I am in the mood for wild similes today.
Anyway, this was just one of the reason university libraries used to hate Elsevier's guts. Do a quick google search and you'll find the whole history. Including how disappointed people were when they bought the good old Mendeley.
As a start:
https://www.theguardian.com/science/2012/feb/02/academics-boycott-publisher-elsevier
https://www.theguardian.com/higher-...r/10/elsevier-buys-mendeley-academic-reaction