According to Edith Reiter's 2014 book, this instrument was completed on 10 October 1906 and sold to a customer in the USA.
Howe & Hurd (2004) describe heckelphone #25 as a model 36a that has later been modified, by Alfred Laubin, to a model 36k. As of 2006, it was reported to belong to the New York Metropolitan Opera, where it has been played by Andrew Shreeves. It has also been played, more recently, by John Upton.
The history of heckelphone #25 remains largely unclear, but it is possibly the first heckelphone sold to the USA.
Heckelphone #25 can be seen and heard, played by John Upton, in this video.