As I mentioned earlier I was pretty interested in this as nothing else with sufficiently good end-user experience exists in the Qt world. There is the Qt Installer Framework, but from what I've seen in Qt Creator, that is designed for developers - pulling people through wizards is not the way to go in 2017.
I've implemented DBLSQD in Mudlet, an open-source project (code available). We use DBLSQD handle the server-side part of running an updater - provide a feed clients can check for new versions, and parts of the client-side as well. On the client-side, it handles downloading of the new binaries, showing the update window, and a changelog window post-update.
Installing updates is complemented by Squirrel on Windows and since we use AppImage on Linux, no installation is necessary there. I did find it too difficult to integrate with Sparkle on macOS given by lack of Objective-C knowledge that Sparkle required, on macOS we use Sparkle entirely and DBLSQD provides the feed for Sparkle to work with.
So, overall, I'm super happy with this! Finally been able to add an updater to our application and @pentacent has been super helpful throughout the process. He's super responsive in communication, he adapted dblsqd to fit our needs, and he was also happy to include contributions we made to the clientside code. If I need an update solution for a commercial project, I would be more than happy to purchase a plan - the tech is good and support is top-notch.