I bought one of these a while back as a curiosity, I tried it with my MiSTer and while it worked it was a little bit laggy for games with a bit of screen tearing.
Saying that, it has proved to be useful for work, I've been able to use it to write documentation and capture screenshots and videos of things like BIOS and UEFI settings screens and as mentioned by another commentator it's handy for headless systems not having to have a monitor kicking around. For the price you can't really go wrong and with it's small size it's easy enough to keep in a laptop case or tool kit.