ReadCube has been a useful tool to read some papers that I don't have access to but what is it like as a reference manager? How does it compare to Mendeley or Papers?
Readcube has some really amazing, unique features like enhancing the pdf (which export all the paper's references automatically) but it's not the best till now. it becomes the best if:
1. Add "watch folder"
2. Add "nested folders"
3. Offer a free cloud version (The sync on the cloud is only available for premium users)
4. Add the ability to import important formats such as *.bib, *ris*, *.xml and etc. Readcube can import pdf files right now. Which means it's not easy for you to switch to this software if you already using other reference manager such as Mendeley or EndNote or etc.
5. The reference managing ability is only compatible with the word (You can also export to bib file manually)
6. Although it has very nice annotation style, it doesn't export these annotation styles in standard PDF formats. In other word, you can't open annotated pdfs using standard pdf readers such as adobe, Foxit or X-change viewer. If you are familiar with mind mapping reference managers such as Docear.
Finally, my opinion is Papers is the best, but it's not free. So the best candidate after Papers is Mendeley which can cover everything you need.
Readcube has some great features. The ipad app is stable. The developers are suppose to integrate readcube and paper3 for mac app. The app is scheduled to launch in early 2019 but still its not here. The native mac readcube app is not stable. You can add a pdf to readcube and it automatically gets the citation information but sometimes for some papers I have found that it fails to gather information. There is an option to mentally resolve the issue and it fails annoyingly. Nice features for reading paper, taking notes and annotating.
Overall it is really good. I believe the development team is not very active to solve the bugs.
Readcube has gotten much better but it's predecessor (Papers 3) was better, in my opinion. Standalone MacOs app is stable and works but using it as citation manager outside of Word is pretty much impossible (Magic Citations in Papers3 was much better). The app is also more of like a web interface (not exactly, but I don't know how to describe it otherwise). It doesn't have robust menu options (almost none, really) and you have to point and click for everything. Also can't cut and paste when editing metadata. In short it works, but is a long way from being truly great.