It "clicks" when you turn it so its easy to switch between boost levels. Has the soft spring in it, lost the other spring. I ran 26psi with it, would go higher but not sure how much. Comes with mounting bracket.
For the record, mine with the soft spring would not go any higher then 21psi. I also lost the stiff spring. I emailed them and they shipped me a new one free of charge. Great service.