Maybe it's just a psychological thing, but I feel way more comfortable gaming on a dedicated device than my phone. I don't have to worry about losing all my phone battery, or getting popups and calls while playing, or having to exit the game to check messages etc... It's way nicer having it just be a handheld that does one thing well.
why did you pick this handheld instead of many others?
Form factor is the big one. I think the Magicx is basically the same size, I was also looking for something that would fit in my pocket without much issue. It's funny that you mention Android as a reason to buy one, I specifically looked for one that WASN'T Android. Linux handhelds are a lot simpler to work with and you don't have to worry about Android shenanigans like processes running in the background or having to sign in to Google and update apps etc...
For me, most of the games I'm interested in playing are SNES, GBA, PS1, and some PSP. If you're looking to play PS2 or higher then yeah a more powerful Android handheld makes sense, but I didn't care for it that much.
This has more to do with the Windows frameworks costing an extra $140. I'm sure a lot of people will just buy it with Linux and then 'obtain' Windows on their own.