two-phase 50amps electric switch
The problem is, the pretty ones you saw there are Chinese junk.  You can't safely fit a 50A switch in an Au/UK 1-gang space, it needs more airspace than that to arrest arcs. 

This need for a shutoff switch is a common one, and you can use any variety of air conditioner or outbuilding shutoff switches or hot tub mini-panels.  In some of them, they are simply a 2-space breaker panel, and the breaker is the shut off switch; a breaker is the cheapest 50A shut-off switch made.  

You may use any device rated 50 amps or more; there is no need to match the size of the equipment to the size of the load. The 50A breaker in your main panel will protect your 50A equipment regardless of any higher-rated devices in the chain.