So these are ok, as long as you don't mind not having any swifts move in, or having it last more than 5 years. A well known and peer reviewed local expert who has had incredible success, gives talks about swift boxes, installs callers etc, absolutely detests these. Sadly, I bought one before he came and did a survey. It is apparently designed poorly, with too narrow a base for the nest, and the entry hole is too small & high up the face, so it 'might' attract some swifts, in 3 to 5 years, but it's also fairly poor quality so unlikely to last long once they find it. I've actually got two because the first one was so badly packaged it was damaged when it arrived, but a capable carpenter fixed it up. Happy to edit this review if I get swifts in the next year or two, but personally would not recommend or buy again.