Japanese saddle purveyors Kashimax have the stateside cachet of NJS certification: a growing contingent of Keirin fetishists in urban areas won't settle for anything less than that which has been deemed race-worthy in the Land of the Rising Sun.

That said, there's no indication that this interesting fender design, brought to you by none other than NYC Keirin specialists Chari & Co., is intended for velodrome use... though it is certainly preferable to other rain gear we've seen. The "Rain Tail" is a telescoping fender that is fully concealed under one's saddle when not in use.

Curiously enough, Chari have opted for a non-NJS saddle and frame for their product photography... though this simply might be to demonstrate that it works on certain non-Kashimax products as well: "we are still not sure which saddle can fit this fender. We verified this fender is attachable to: Kashimax (43mm), San Marco Rolls Saddle, Fujita Compy and Selle Italia Turbo."


As something of a purist myself, the discreet—and presumably discontinued, as it's listed as "Dead Stock" on Chari's website—design intrigues me... though I'm skeptical about the attachment mechanism, which seems to allow for a bit more rattling than I might care for. (That, and the fact that I have a backup Bookman tucked into the space between my seatpost and saddle... though my Knogs are still my go-to lights.)

While we're on the topic of thinly-veiled-but-well-intentioned plugging, Kashimax recently produced a nice promo piece on their saddles (following the trend of production videos):
In any case, I'd been meaning to pick up a fender to complement my sweet rain pants, so maybe I'll give the ol' "Rain Tail" a go... if, of course, it fits on my saddle.

via Chari & Co.
Comments
I'm going to call baloney on this fender. The fender itself is very thin and it sits pretty far away from the rear wheel when deployed. As someone who has ridden in the rain I have serious doubts about its liquid filth blocking ability.
Hilarious. I always wanted a dry thin strip on my back back when cycling in the rain.
Ben I completely agree it is anadequate. The narrow "fender" is too far from the wheel to protect the back of the rider from wheel spray. The idea that a fender could extend from the saddle when needed and tuck away when not in use has merit though. Could an expanding fan concept work here?
A good idea - retractable 'fender' (though i'm not sure how retractable it would be covered in mud)
Implemented poorly - WHY make it a saddle-based attachment? A bad idea for the reasons others have pointed out.
= maybe the definition of bad design.
I wouldn't say it shines well on the Core to make it a feature.
There are so many of these kinds of emergency fenders being designed right now, and this one is probably the worst I've seen. Show me a foldable/collapsable fender that actually performs closer to a standard one and I will be impressed.