We just installed an XR18 in my church. I have been using it with my iPad Pro. I have seen it connected to android phone, small android tablets etc. There really is no comparison to the UI on the iPad. FYI the XR18 comes with a small controller pad, or at least ours did. The sound is much better if the person using it knows how to properly EQ
and use sends to the wedges. Problems usually boil down to user error. It's much easier to make a mistake with it or struggle with the GUI if you're attempting to use a phone instead.
Concerning the signal dropping out. It's only happened a few times using the built in wifi. Once I think it was because too many people were on it at the same time. I am thinking about getting another wifi access point hooked to it just in case. Really though, it hasn't been much of an issue here. Things like low batteries and being too far away can contribute.
The tech told me that the preamps were "midas designed" not really midas. Not sure what that means? I thought since Behringer owned Midas they were, in fact, midas pre amps. They sound quite good.
If i were going to go with the Presonus using the built in SD card for recording I wouldn't get their lower end model. There have been nothing but problems with those. Shoddy cheap construction, they don't sound very good and they haven't held up. OTOH their higher end mixer with built in SD. I've heard nothing but good things.