Personally, while I don't think that Alaska will add them anytime soon (particularly since American, the US legacy carrier which they have the closest relationship with, also isn't planning to add them,) I do think that it provides a more premium experience. Sure, my phone or tablet might be a few years newer, but the screen and software really doesn't need to be super robust or "up-to-date" anyways. As long as the software is built well and supports playing the in-flight entertainment and route map well, I'm not worried if the software and screen was basically solidified five years ago. They don't need to run all the latest and greatest apps for a bunch of different services - everything's in house and just needs to be built to support basic streaming functionality from the on-board entertainment server.

For me, I like having that second screen so that there can be something in the background while I'm using my main device, or simply to free up space on the tray table. A quality seatback tablet holder helps with the latter, but it's still not perfect, and it still requires me to have brought a tablet. If I just have my phone with, or a phone plus a laptop, I no longer have a device with me that can be off the tray table and a suitable size (in my opinion) for watching a movie on a flight. Plus, there's still more tasks for me to have to do to get everything ready for the flight (make sure I have all my preferred content downloaded to my device, download the proper app for the airline, make sure it has a good charge) versus seatback entertainment, which is just there and ready to use. I've also had issues on other airlines where even if I thought I did everything I needed to do (even downloaded the app) I get on board and the BYOD entertainment just doesn't work for some reason. Sure, I can still use anything that I downloaded personally, but it's still frustrating.