Are Russian sites dangerous?
You can find lots of things at Library Genesis. http://gen.lib.rus.ec/
Yes, but it is a Russian site. So, be careful.
Not this one, no. This one is basically Pirate Bay for books and is highly regarded by users.
More problematic are those with pirated games and software.
I've used libgen for years and have always trusted it (after my first few times there, of course). Used it to get thousands of digitised versions of books (that I own) and some that were simply unavailable anywhere even in print format. Also used it to get the translated version of some books too. Very useful.