On the flip side of traveling with only one device versus just having a second device, you now have the downsides of one device: now you’re using one device for everything so you’re draining the battery of that one device and only one person can use that device at a time.
When I travel solo I take my AYN Odin 2 Portal with me for gaming. That thing has a battery that’s twice the size of a typical smartphone and it can play games pretty much all day before the battery dies, while my phone is in my pocket fully charged ready to be useful at my destination.
If I played games on my phone during the plane ride I’d arrive at my destination with a seriously depleted battery and charging anxiety, or I’d need to travel with a spare battery.
Is this setup bulkier than an iPhone Duo? Sure. The AYN Odin 2 Portal is also a $230 device.