The Bonfils is a rigid fibreoptic intubating endoscope, which can be used to provide fibreoptic assisted laryngoscopy, or as a single device for intubation. Both the midline and retromolar approach can be used. It is well suited to patients with high-grade laryngoscopy (Cormack-Lehane grades 3 and 4), patients with limited mouth opening, or floor of mouth masses. It cannot be used for nasal intubation, but can be used through some specific supraglottic airways.
Karl Storz have a useful ‘Silver Book’ on the clinical use of the Bonfils, which is fully referenced. You can request a physical copy from them or download the PDF here:
McGuire & Younger published a CEACCP article in 2010 which addresses various forms of indirect laryngoscopy, including some (not all, alas) of the rigid intubating endoscopes. It is open access on the BJA Education site.
Thong & Wong published a thorough review in A&A on the device in 2012. You can access it free here on the journal site (Open Access!)
Basic overview and fibreoptic-assisted laryngoscopy:
3.5mm Bonfils intubation in a child with a severe sub mental abscess (read more about the case here):