One major headache with Nvidia's menu is that it doesn't recognize apps unless they're loaded directly from the Google Play Store. However, we get IPTV for our local, Canadian channels through a local provider, Surf Internet. Unfortunately, their television app must be sideloaded. Even getting the APK file onto the Shield for installation took a little planning. I set up the Nvidia device to share files on my home network; therefore, I was able to drag and drop from our main Win 10 computer.
Next, I had to search around for an easy way to access Surf TV through the menuing interface. The most elegant way was to use the online app atvlauncher.trekgonewild.de/index.php and build an additional APK.
I had nearly decided to simply use a side-launcher app. They are ugly and not very good at determining which apps should be included. My results were definitely worth the effort and now I do not fear the thought of sideloading any apps not exclusively designed for my Nvidia Shield TV.