Hi,
Yes, I can confirm if the site is legit. I downloaded the firmware myself and extracted and it contains the firmware including windows clean install
Also, if you want to download from baidu, you need Baidu account and its downloader.
Y0u can also download KNote 5 firmware using shared link by @winterless here https://techtablets.com/forum/topic/alldocube-knote-5-audio-driver/#post-144424
Regards
edit : also check the official site instead http://www.alldocube.com/en/support/support-info/#system-update?tx_post_tag=intel