Here are some random issues I've been dealing with, and solutions.
I recently discussed full Android smartwatches and their uses. These watches will run any Android app, including listening to streams, music transferred to the watch, even viewing movies.
Well, it turns out that putting stuff on these watches is no easy task. Even though you can install and run file manager apps that go out onto your LAN, and pull in files, the actual mechanics of doing so on a 1.5 inch or so round screen are difficult and time consuming. I solved the problem by installing an FTP server app on the watch called Primitive FTPd, and then transferring the files using an FTP client (WinSCP) on the PC.
Another problem cropped up in doing so. My router uses dual band WiFi (2.4 & 5 Ghz). The watch only supported wifi with 2.4 Ghz, and I was continually getting network errors in transferring files, and the transfer rate was really (and I do mean really) slow. These errors didn't happen with anything using the 5Ghz wifi, and it's fast. I went from suspecting the wifi chip on the watch, to the apps, but finally looked at my router and noted that the 2.4 Ghz network used 'mixed' protocols - 802.b, g or n. I changed it to 802.b & g only, and voila, problem fixed! No more network errors and transfer rates sped up substantially as well.
I'm now busily putting music on the watch (encoded at 24kbps opus mono with full range sound) and gradually filling up the 128GB. The built-in music player supports opus, but I also have foobar and other music players installed on the watch just in case. I use foobar to stream Artisan Radio.
You have to use bluetooth earphones, unfortunately (the watch does have a speaker but the quality leaves a lot to be desired). Bluetooth works flawlessly (in fact, better than on my various PC's, where bluetooth tends to be a weak point).
The watch will use my sim card and connect to my carrier (Telus), but I leave the sim in my phone (the watch works fine without a sim, you just have to use wifi and bluetooth for connectivity).