I have a portable monitor that I’m pretty pleased with.
It has a magnetic cover that goes over the screen to keep it safe, and that same cover folds and goes on the back to act as a stand when it’s in use. Power and video are via the same USB-C cable.
Nice and slim and stays in my bag most of the time but when I want a second screen I can whip it out in two secs.
A screen that attaches to the laptop sounds convenient initially, but I feel like in practice it would be a hindrance and make your laptop clunky and bulky.
Yeah but there’s clunky in the way where its big but still a single unit as designed and intended, and clunky when its got some extra growth hanging off the back of it like some technological parasite.
Of course, my advice is only that, and you should choose the approach that works best for you. But advice is why you came here right :)