I have a 20 amp relay running mine. That magnetic clutch looks like it would draw more than 5 amps, which most 12v switches are rated @ 3a. It may be overkill but when your changing a flat with your impact gun in -20 degree weather, you won't be complaining.
No I don't have a relay laying around, but as I was re-wiring some of the truck last night, I realized it may not be a bad idea to install one hooked up to the ignition circuit so that I don't overload the ignition circuit with all the accessories that need a keyed line(radio, CB, lights, York). I figured I would go get one of those 3 or 4 pole Ford starter solenoids, and I could hook up as much to that as I wanted without fear. I probably should get an extra fuse block.
Turns out that even without the York, I'm already drawing too much current from the ignition circuit. When I flip on my 2 Hella's my radio cuts off then back on from the voltage drop. Time for a relay.