The Gueneau S-001 is a rather interesting item. Probably evaluated by the Swiss AF with the aim to provide pilots with a "Super-Leichthelm" (Super Light Helmet) by the end of the '80.
Unconfirmed sources claim that it was designed by Gueneau with the support of Intertechnique during the R&D process of the EROS MP90/91 oxygen mask and related helmet-fitted connector receivers.
During the tests carried out, the helmet was appreciated for its lightweight and comfort, nevertheless a number of problems arose: given its design, the failure to maintain size adjustments, doubts about its protective capability, the protruding visor handle that interfered with the upper Mirage III ejection seat firing sequence initiation handle also threatening to scratch aircraft canopies; and the three attachment points of the the mask harness (EROS MP-91), difficult to use.
It looks as if those helmets were planned for the American and possibly Swiss market. Above problems and reportedly unbalance issues (?) stopped their development.
the definition S-00x (S - Suisse?) simply identified an helmet and not its model (unknown to date) - The manufacturer supplied three helmets (S-001/002 and 003).