nestbox attached to cage

Hi there everybody :) - I want to discuss a problem i have with my cockateil pair. Male is a heavy pied and female is a pearl. - Pair is confirm as Male whistles and female is always silent. - Not sure of age but I have them for last 6 months. - Male looks inside the breeding box but never...

I am currently trying to decide what type or brand of nestbox to use. Any suggestions? I have added links to the ones I am interested in. The box will be mounted on the outside of the cage...