I bought the Stealth Pocket for my top tube to use in addition to a larger seat post back that holds my spare tube and other repair items. I use the Stealth Pocket for more frequently used items such as gels, chews, tablets, etc. that I can even access while riding or quickly grab during a brief stop. The bag is narrow which is aerodynamic but that does limit its capacity so you have to make some tradeoffs in what and how many items you can pack.
Great appearance and it's made very well, but it's odd shape limits the stuff that will fit inside and it's a bit $$. I carry a multi-tool a small can of pepper spray, and my house and car keys. Since I went tubeless I don't use a seat bag anymore and I needed something. It doesn't attach to the head tube and will spin around and end up hanging on the bottom of the top tube unless you attach it. I used two strips of Velcro between the bottom of the bag and top tube and it did the trick, A 55 for the design and construction and a 35 for the lack of attachment to keeping it from spinning on the top tube.