Any reason they cost so much? I have one of http://www.ebay.com/itm/231281787368?_trksid=p2060778.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT I used for a different project. I added a gauge and adjustable pressure switch for a net cost of around $60 today. Can I use it, or is there something about those $300 units I'm missing?
