Luther H. Dyer's book The Problem of an International Language and its Solution in Ido

The book has recently moved to this link, and it's definitely a book anyone interested in IALs but uncertain which to learn should give a read through. The part that best explains the difference between Ido and Esperanto is found in the two links here and here, especially in the second where reversibility is explained. Reversibility is one factor in Ido that really appealed to me in 2005 when I first started learning it, as it resembled a few other languages I had learned such as Japanese, Korean and Turkish. See a comparison of mine here.