Good question. They don’t make this obvious, but:

- you don’t get the article, you get a browser window

- they only have about 1/2 of the articles (!)

Quoting from their FAQ:

Q. What does "renting" mean?

Renting articles is the simple and affordable way to get the high quality articles that you want, with the same layout and formatting as the printed or PDF versions.

"Rented" articles are available through DeepDyve's cloud-based service and can be viewed through your browser from anywhere you have an internet connection.

Read full text articles as often as you want during the rental period, and depending on your plan, you may print a limited number of pages per month. However, rented articles cannot be downloaded or shared.

Q. Why can't I rent, download, or print some articles?

DeepDyve works with many publishers but unfortunately not all of them have given us permission to let our users rent, download, or print some/all of their articles.

If an article is marked as "Preview" it means we only have permission to display the abstract but nothing else. As for downloading PDF’s, approximately half of the articles in our collection can be purchased and downloaded directly from DeepDyve. For the remaining half, DeepDyve provides a link that takes you to the publisher site where you can purchase the PDF directly from them.

True, but you can store articles in folders online and bookmark them. You can print a certain number of pages per month - 25, I think, and that adds up. Is it really necessary or even useful to print out or store locally?

It seems like their viewable content is 20% of the available literature, and the coverage is increasing. They appear to have recently added APS journals current up to five years ago. Adding arxiv to that, the physics coverage is pretty good, especially for historical research. (You also can access APS journals via your local public library.)

Is there a list of journals or publishers that are on Deepdyve? Seems to me that the only way to know if an article is on there is to sign up.

Yes, look at https://www.deepdyve.com/browse/

As an example of a topical search with no login:

https://www.deepdyve.com/search?query=COVID-19

Another search:

https://www.deepdyve.com/search?author=Doyle%2C+W.+T.

And a page from that search:

https://www.deepdyve.com/lp/american-association-of-physics-...

You get only one page when not logged in, but Deepdyve has all of American Journal of Physics, which is really nice.

Deepdyve has been submitted several times to HN over the past decade, but it never generates any interest. That's surprising, considering the interest in SciHub.

You can't read the full text w/o signing up for the free trial. Without registering, you can't bookmark articles or add them to folders, either.

Depends on the field. For example, none of the IEEE or AIAA journals are available there.

Yeah, IEEE is always a problem. Even IEEE members have to subscribe to individual journals, and there are a lot of them.