One of the reasons why experts recommend learning Esperanto is its propaedeutic value, which has been the subject of several studies. However, Esperanto is not the only (international) auxiliary language; other examples include Ido, Interlingua, Afrihili and Interslavic. (Some call Interslavic a zonal constructed language, but the distinction between zonal and international is not relevant here.)
Hence my question: Are there any studies on the propaedeutic value of international auxiliary languages other than Esperanto?