The problem with milk auto-frothing devices on espresso machines

I was copied in on a email today about a complaint made by a customer over the quality of a cappuccino that he had been served at a particular food-service outlet. His complaint was that the drink that he had requested had just a small covering of foamed milk, and was not thick and creamy as he had expected.
The particular outlet uses an "auto-frothing" device that is attached to the steam wand of the espresso machine. The reason they and now many domestic machines use such devices is to make the production of foamed milk quicker and easier to deliver. Dare I use the word "de-skilling" the job.
Now auto-frothing devices are fine if they are kept immaculately clean. The reason I put this caveat in is because Jersey Milk with its higher than average fat content has a habit of clogging up the minute holes that enable the steam to combine with air to create the foam. Once one of these holes has become blocked rather than creating foam you end up with hot steamed milk.
The discussion went on about how different types of milk foam better than others. That may be the case, but the difference is not as significant as some people might think. I've always found that full fat and half fat milk both produce equally good quality foam if heated correctly.
No the real problem lies in the on-going maintenance of the auto-frothing device. In a commercial environment this means setting in place procedures to ensure that the device is either replaced with a clean unit or stripped down regularly depending upon volume. More often than not problems occur just after a busy period when there is an opportunity for the milk to slightly congeal.
As far as domestic devices are concerned these should be stripped down and cleaned after usage. This will not only ensure that the frothing device continues to work properly, but also eliminates any hygiene problems.