Hey Rob, I bought one of those but don't find it helps me much. It certainly doesn't hurt with foaminess, but it just is messy. After I'm done filling and close the tap, I find there is beer still in the growler filler tube, presumably because of physics? Anyway, as soon as I pull that filler off the tap... bam... beer on the floor.
I've found success lately by doing what Roger does... cold water rinse, turn the PSI down to 4 and I fill off the tap directly. This is just for quick consumption though. I have a blichman beer gun for long term bottling that works good once you figure it out.