On the VED front, I have a manual cheap one from Temu which is manually controlled. When I use it, I start with low pressure just to pull my tiny todger into the tube and leave it for a minute to start to grow. Then a few more pumps to apply some vacuum.
There is a tendency to overpump to see if we can get it back to the pre-op size and that is a mistake - it can become very painful. So I wonder if the battery automatic ones are just applying too much vacuum and are thus quite painful at the beginning.