Avira is lighter than bitdefender but u dont need the extra engines. Just try and install it. better test it urself instead of ask all this questions. it can behave not the same from system to system. if u dont like it or feel it slows down ur laptop simply uninstall it. Qihoo is autopudating but it have a delay,sometimes some weeks but it is not needed to updated always the same day to the newer version if the old version works without problems u can just wait untill it get auto updated.