We've been using the udderly ez for 5 years and we have not had any problems with it harming the goats teats.
And if you use one you realize the vacuum isn't constant. You pump it up and when it gets to a point and the milk starts flowing, you stop the pump. The pressure on the vacuum at that point starts to gradually decrease. As the flow of milks starts to slow down, you pump it 3 or 4 times and it increases the vacuum again.
We used the 1 cup containers instead of the larger containers, they fit under the doe better.
It usually works with us that when we start on one side we apply the initial pump up and vacuum. The milk will flow, then start to slow down, so you pump up 3-4 times, milk flow increases again. It starts to slow down, so you pump a few more times. At that point, that cup container is full. That whole process took less than 30 seconds. So, we stop, empty the cup container into our quart jar and repeat on the other side.
So, you aren't applying the vacuum to them for very long periods at the time.
Does that make sense?