Raymond S.wrote a review of Castelli Undersaddle XL Bag on November 2, 2015
Familiarity: I've used it several times
With this bike I carry a tube,2 tyre lever and bike tool. And still have small free space.
I just use it for 3 rides, each around 100-250 km ride. The shape is perfect for road saddle even with long oval shape f8 seatpost or common seatpost. This saddle bag not make discomfort when pedaling. I haven't test it on wet weather yet. I hope soon rain will fall and try is this bag good in bad weather. Tx