I am using a Asus Zenscreen as my secondary laptop monitor.
Having dual monitors on the go is great. I spend a lot of time in online meetings and having a second monitor is really, really good. Meetings become so much more productive when I can work with several monitors. The Zenscreen however, has it’s drawbacks. It’s another thing to lug around and it has it’s own case. And it needs desk space. And takes up the only USB-C port I have on my non-framework laptop.
A good dual monitor laptop on the market would probably be a niche product but it would be a nice niche.