i have the mate 9 and nova launcher prime, on my phone it sticks to nova launcher, you have to set the default to nova launcher and then keep pressing the back button until you exit the setting pages. If you close the settings after it may create problems. Also, you can set default voice control to google launcher3 this will enable google now to be on all the time and on any screen. This works well on my phone. Also if you install google Allo app, then you will get google assistant on that app, so when you say "ok google, open google allo app", you will get google assistant. My experience with the mate 9 has been good, but overall i think the galaxy s7 edge wins hand down. If you are considering getting the mate 9 pro, then dont, get the s7 edge and then upgrade to s8 that will be launched in march/april 2017.