We have used a few on customers cars. The biggest issue is they are a bit bulky and consequently hard to hide / locate. They work in conjunction with available engine vacuum or as a stand alone pump. They do have a vacuum switch that shuts the pump off above a certain level. Relay wise a 30A unit is way overkill.
I do happen to have one sitting on the shelf that was installed and removed due to an unforeseen engine swap. PM me if interested.