I've been using Stella Launcher on Nexus 5 for a while now. Originally I was skeptical about the whole concept. Jolla's UI is just so different than Android's so how could it be a good experience to have launcher from Jolla and then just normal Android UX in apps, system, and settings? Also because of Android API restrictions the launcher could not support all the things Jolla's homescreen has, so even the launcher is not 100% same as homescreen experience in Sailfish OS. There are some rough edges, but all in all I'm positively surprised on how it turned out. Personally, I prefer using Stella Launcher on my Nexus 5 over having standard Google launcher.
I think I prefer Stella Launcher because it makes the homescreen simpler. There is just my apps and running apps. No widgets, no app shortcuts, nothing extra. All the apps I rarely use are in folders so my app grid is just one page and I get to apps I use often really quick. The one thing I'd like to see improved is the integration to Android notifications. It would be really nice if access to Android's pulldown notification menu could somehow be improved.
It's great that with Stella Launcher wider audience gets to explore a bit about Sailfish experience.