I have used them before and had a few waterpump seals leak right after filling due to vacuum pulling on it. I can say they must have been weak to start with , but just the same.
Usually a bleed hole in the T stat and unhooking a heater hose is more than enough to get the air out of practically any car.
A lot of the high pressure shops like to have the big cylinders with the valves that make it look complicated, so the customer sees it , and thinks he is getting something for his 89.95 cooling system flush.Thats why they have them...customer percieves value when a big complicated machine is hooked to there car.
I wonder why its different when you hook up a 15,000 dollar scanner and charge 65.00 bucks for that plus an hour of testing, why they complain.....?