I definitely wouldn't recommend those attached screens. They're small, bulky, usually have low quality displays and none of them can be used without a kickstand, at which point you might as well get a portable monitor instead. They come in a variety of sizes, with many different features (OLED, touchscreen, speakers...) and at many different price points.
I used a 17" DIY portable monitor for about two years when I didn't have a permanent workspace and the only complaints I have about using it are solved in most commercial models, I just stubbornly wanted to use my own. Just be careful with the cheap ones as they often have the same problems: poor viewing angles, no backlight adjustment, wobbly kickstand, multiple cables required....
I used a 17" DIY portable monitor for about two years when I didn't have a permanent workspace and the only complaints I have about using it are solved in most commercial models, I just stubbornly wanted to use my own. Just be careful with the cheap ones as they often have the same problems: poor viewing angles, no backlight adjustment, wobbly kickstand, multiple cables required....