You pasted a HTTPS address, but the server doesn't answer to HTTPS (it is somewhat redundant when you use onion services anyway). The correct one is http://scihub22266oqcxt.onion/
It's not redundant; if someone sets up a malicious exit node they can view all your traffic, unless it is encrypted e.g. by SSL.
Of course for this kind of site that is not so important, but you shouldn't use any kind of site where you log in or enter sensitive information over Tor without HTTPS.
It's fully redundant for .onion sites. Traffic destined for them never goes through exit nodes. It is only ever encrypted in a way that is readable only by the specific .onion destination.
Image: http://i.imgur.com/xZmDmPY.jpg