I use the xr18. I also run it in the house as the heart of my studio! I love it.
I use the internal router at home and never had an issue but I do have an external router housed in the 4u rack as I don't totally trust the internal one. It's never failed at home though!
I also have a mini pc running reaper so it's always ready to record .
Nor got experience of the xr16 but the extra aux mixes were the deal breaker for me. And, the drummer cam go stereo in ears to get a bit more audio separation in his ears. Well worth the extra money even if you don't instantly think you need 6 monitor mixes.
The unit has never failed or crashed on me and its probably seen 300 hours of use.
Regarding the app. I actually prefer the behringer app over what most people recommend using, mixing station. Although it does take a wee bit of patience to get your head round but one you do it's pretty straight forward.
I have a 'show' setup for home studio and another for live. In live I then have a blank scene, then multiple different scenes for places and rehersal rooms we've played. I then can just pull up whatever mix we used last time! When I go home I then just pull up home studio and it's ready to rock.
I also change "layer" from home use to live use. That is essentially how the app is laid out. For band which is always just for iem mixes, I remove everything g other than the 7 channels we use, and then the 4 effects returns. So dies the other band members. But I also save a different layer for home use and for a full desk if I'm running foh.
Dunno why I rambled on about the app, but there ye go.