I tried out that windows phone continuum feature back in the day to try and get actual work done. Here's what I remember of it.

You could connect it wirelessly to your windows laptop and it would take over screen, keyboard and mouse from the laptop. The actual connecting part worked smoothly, but it could only stream one relatively low res screen and even then over a wireless connection it felt sluggish. I couldn't use the laptop while the phone was connected, and this was its biggest handicap because I would have preferred the phone's desktop in a window similar to running a virtualized OS, with easy drag-and-drop and copy-paste.

The experience was that you had the same phone apps with the same feature set as on the phone, but they transformed into desktop layouts. For the first party apps this worked fine, but many of the third party apps didn't work at all or didn't work well, so I ended up largely being stuck with the first party apps, mostly the mobile versions of Outlook and Edge, and the file explorer. At the time these were seriously limited compared to the desktop counterparts. In that version of Edge I couldn't use many of the web apps that I tried. The outlook version was very basic, but I still managed to get some of my email done.

The apps only appeared fullscreen. I get why they did it on the weak phone hardware of the time, but this was very limiting. You could alt-tab however, and there was the windows taskbar. The start menu was the phone's home screen, so you would see the exact same tile layout as you saw on the phone, and clicking a tile would open the app. I really liked this solution because it gave a lot of flexibility while being instantly familiar.

Bottom line it wasn't really suited at being a one stop computing experience, but it was a good way to do the things you would otherwise do on the phone on a larger canvas. It was good for what it was, but it was not in any way a laptop replacement. What really killed it as a useful feature for me was what ultimately killed windows phone: the lack of a decent app catalog. I still think in its time windows phone was the best mobile OS, but the app gap meant that it never stood a chance.

I kind of doubt it did work well for them. Microsoft was having an identity crisis at that time where they didn't yet realize nobody wanted their tablet UI on desktop.

If they allowed straight Win32 ports on ARM it could have been interesting. Or if they did it now, where I think x86 emulation on arm is working well these days.