Hario Switch
It is officially named "Hario Immersion Dripper Switch", and very hard to find outside Japan. Kurasu is a good place to order online.
I love how this brings a bit of immersion to the V60 game. It helps to serve a stable cup since agitation is made less important. The simple metal ball mechanism is ingenious and reminds me of the Pachinko machines, the ground zero of the Meditative Games.