I had a Unity Atom demo unit for the last few days and actually just ended up buying it. It's a great sounding and versatile little box - the app on the other hand, is not without issues.
When initially setting up the Atom, I quickly switched from a wireless to a wired connection, as it made things a little more robust and easier to troubleshoot. But I had a lot of trouble getting the app on my phone (Android v7) to find the Atom. To make a long story short, as a last ditch effort, I installed the app on an old phone of mine and there it started working. So, after looking into IGMP snooping and the output of the Net Analyzer app on my newer phone (I skimmed through the forum here), it dawned on me that the VPN that I'm running on my phone could be the culprit. I'm using the VyprVPN app, but it is configured to connect only with unknown WIFI sources, plus I explicitly configured the NAIM app to bypass the VPN. Nonetheless, things only started working after I force-stopped the VPN app. Maybe someone struggling with the setup might find this useful.
Still, in terms of reliability and robustness, the Naim app could take hint or two from the old Squeezebox/Squeezeserver (which I run for years without issues). It often happens, that my UPnP server fails to show up in the app (btw: why does the front panel interface lack the 'server' blob that the app has?). When I force-stop the Naim and restart it, the server shows up again. Sometimes, I can open up VLC on my phone, navigate to the UPnP server (which VLC finds without fail every time), and after that it shows up in the Naim app again. I also hooked up an external hard drive to the rear USB port, but even that sometimes fails to show up. I suspect, this might be due to the HD going into sleep mode and the Atom fails to wake it up (?). Doesn't seem to be an issue with a flash drive plugged in. Also, it's a bit irritating, that the favorites on the app home screen keep refreshing every few seconds. So, if I scroll down the list, I'm back at the top again, when it refreshes.
That little Atom sounds great and is a lot of fun, so I'm putting up with the above issues (I bought it afterall). But would be nice, if it were a bit more solid in the app department.