I can’t understand that all positives reviews. It asks to have premium account to full use it ,otherwise only 15 minutes of video are allowed.

I am genuinely confused as to where all these positive reviews are coming from?
It lets you choose guest mode if you don't want to create an account with them but does not let you do anything without first logging in.

Once you actually log in, the interface that was detecting the videos and giving you the option to download them disappears with the only things being present being the premium plan.

Just another case of wasting people's time by presenting an extension that does nothing without the premium plan which only becomes obvious once you've gone through the hassle of setting it all up.