Get the air actuated one from McMaster, make sure the switch can handle the load.
OSHA doesn't like electricity near water very much.
This is an important thing to have. Left on, many pressure washer pumps will fail after ten
minutes or so even with an unloader.
The auto-on switches are cool, but can cycle your pump too often, IE spray, stop for 1 second,
spray again. Bad for motor and pump. They have also been the first point of failure on my old cheap
pressure washers.