Erections are still possible but they are confined to the size of the cage that he is wearing. When erections happen, it will feel very snug and perhaps slightly uncomfortable until the erection subsides. After a few weeks, the body will limit the amount of erections that happen but they will never go away completely.
Once you remove the cage, erections may take up to 24 hours to be back to normal. Until then they may feel less firm than normal. For men with erectile dysfunction caused by performance anxiety, male chastity can often help with these types of challenges.