It is shown de-activated here...
...but it has worked fine for me.
It never lets the boom get away from you, and yes, when you alter the mainsail sheet, you have to adjust it again, and when you throw a tack or a gybe you have to walk it over to the other side. I could run two of them I suppose, but they might get a bit clumsy.
I would not be without it for a moment, it did not cost much, and it got me home to Scotland from Houston.