I have them set up both ways, standing alone near vacs and on the dial in the SS bay. The stand-alones are a total bust. They average less than a dollar a day. The ones in the bay get used quite frequently. I don't have anything metering them, but I hear them running numerous times a day, not scientific, but good enough for me. Customers mostly use them for blowing water out of the nooks and crannies and not the whole vehicle. Bikers tend to like them as well. As an extra service on the bay dial is the only way to utilize them, but well worth it.