Firstly, it works amazingly well. Even better, you can set the playback speed to pretty much any desired value and decide what presets and increments will be available.
What it lacks is a more welcoming GUI. A small indicator hovering over the video would be welcome, for example.
Also, when using 0.1 speed increments, the context menu shows very weird values for speed, e.g. 0.999999999989X when I reset the playback to default.