Will it make his penis shrink?

Yes! His penis may shrink over time due to not being able to fully engorge itself. The Corpus Cavernosa fills with blood and allows the penis to become erect. Limiting the penis’s ability to become erect in a cage will prevent it from being able to maintain its ability to fully engorge itself when aroused. While it won’t prevent the man from getting erect, the penis will appear smaller when flaccid and when erect. A couple good cageless nights will restore it to its former glory as the penis is able to fully engorge itself with blood. There is no evidence of permanent penis shrinkage due to chastity cages. If you want to prevent this, just allow him to sleep cageless once every week or two.