I do like to keep my rear end tidy, particularly on #1 and prefer not to put a light on my seat post as in the past I have had issues with the light fixings scuffing the decals on the seat tube.
The Cateye Saddle Rail Bracket RM-1 is a neat solution to this and also allows me to attach 2 lights when the weather is bad – or on the Winter Bike as here.
The only issue I have encountered is that it does not attach to some of the Carbon Rail Saddles that I have tried in the past as the spread of the rails at the rear of the saddle is too wide for the Cateye fitting (ie the Brooks Carbon Cambium).
Still, it’s a good solution but I’m sure that with a bit more thought it could be made a bit more minimalist.
Given that helmets are now integrating rear lights maybe saddle manufacturers could come up with a way of integrating a rear light too.