People use them all the time for baby hats. There are tons of videos on uTube and several web-sites that have info and how-to's. Also if you go to the Home heading at the top of this forum's page, you will find an section entirely dedicated to loom knitting.
Just received these and already I feel leary about their value. Using the smallest loom to make a baby's hat, I can't believe the large size of the weave makes a usable item. Anyone have experience with these looms? What do you do about it? I forgot to mention I am using two worsted wool yarns together.