PostmarketOS is already in a good state for a secondary device, though I don’t think it can completely replace an Android phone just yet. Most devices still have some fundamental hardware support issues even on the more well supported phones (camera is the big one, call audio is also problematic on a lot of devices). However, as a pocketable Linux machine, it is wonderful. I got a second cheap SIM card so I can have data on my OnePlus 6 postmarketOS phone as there are a lot of tasks that work better on Linux than Android. I keep an Android daily driver but am trying to do less and less on it and more on the postmarketOS device.
PostmarketOS is already in a good state for a secondary device, though I don’t think it can completely replace an Android phone just yet. Most devices still have some fundamental hardware support issues even on the more well supported phones (camera is the big one, call audio is also problematic on a lot of devices). However, as a pocketable Linux machine, it is wonderful. I got a second cheap SIM card so I can have data on my OnePlus 6 postmarketOS phone as there are a lot of tasks that work better on Linux than Android. I keep an Android daily driver but am trying to do less and less on it and more on the postmarketOS device.