Takes some time to boot Android in the container, app compatibility is hit-or-miss, Android apps can't really access the hardware (cameras, sensors etc.), you need to take care to not keep the container running in the background so it doesn't needlessly eat battery up, stuff like that.
You can set up Anbox on your PC and see how that works. It's the same thing on the phone.
It's a Linux container, so no emulation there - but it's still a fully separate user space that communicates with the rest of the system via a bridge in the same way a virtual machine does.
There's also Waydroid, which works by implementing things like Wayland/PulseAudio clients directly inside Android compositor/sound system, but I haven't ran it on the Librem 5 yet (I know that some people are using it on the PinePhone).