The clip-on mechanism feels a bit awkward at first, but actually works really well. Just clamp it onto the upper bout of the violin, and flick the lever. Easy to attach and remove with one hand once you get used to it.
I suppose one could technically keep it there at all times, as it's not getting in the way or anything, but strangely, I find that it slightly reduces the mid range resonance of my violins. I did not expect that to be audible, considering that the device weighs next to nothing, but well, violins are sensitive instruments...