Acestream Engine is needed for any Android device in order to watch Acestreams. Also on KODI, other than the Plexus addon installation you will need this APK in order to be able to stream. No login is required, just install and run it at least once. Then you are set to go!
Using Acestreams apk means you use p2p / torrents so I highly recommend you always use a VPN service in order to be secure. When using the torrent protocol your IP is easy to find so that makes you vulnerable. My recommendations for 100% secure VPN are:
IP Vanish http://bit.ly/1PowS0r
Private Internet Access http://bit.ly/2a2H5gW
Cybersilent VPN: https://goo.gl/LqK4oG