I already had several non-Ortlieb top tube bags, and I wanted the convenience and added security of a quick-release system that would allow me to bring my valuables into a market with me and didn't require me to fiddle with rethreading and adjusting straps each time I got back on.
The Ortlieb Fuel bag and Top tube bag use the same mounting system. Ortlieb offers the Ortlieb Mounting-Set to support the use of the same bag across multiple bikes. But if you are handy with an awl or hot nail, you can modify the bags you already own.
This system works very well in retrofitting other top tube bags. All the hardware you need to attach the quick release to your bike is included. I converted a Timbuk2 bag to take advantage of the M5 frame bosses. The included internal bag fasteners provide enough rigidity to remove the four frame and stem straps from the bag and rely solely on the bosses.
I no longer have to worry about:
1. straps wearing down the bike frame and stem finishes
2. a top tube bag flopping from side to side
3. leaving valuables or an expensive frame bag on the bike when I head into a store or overnight accommodations
Finally, if you pick up a couple of these, you can quickly move one bag between bikes and swap bags on your bikes depending on the ride's needs.
The Silca Mattone is a slick seat pack that has room for my essentials (tube, tire levers, CO2). I like how it attaches to the saddle with a thick rubber strap and the boa closure, so no unwanted rubbing of plastic or metal on the saddle or seat post. I don't understand how it could be accessed while attached to the bike (as claimed by the product description), but that's alright, I would typically take a seat pack off the bike when repairing a flat anyway. I haven't tested the water-resistance yet.
I like the XLAB top-tube bags. They are lightweight, aerodynamic, and provide easy access. No more stopping, getting off my bike, unzipping my under-the-saddle bag, rooting around and hoping nothing falls out. I got the Stealth Pocket 100 for my race day bike. I tried the Stealth Pocket 400c for my training bikes but found it too narrow to hold my training day needs. I returned it and got the Rocket Pocket XL. It has room to hold my emergency tire stuff, my flip phone, hydration packs, with room to spare! And it sits below the top of my headsets for good aerodynamics!
I bought the medium Grid bag. It is a very sturdy and well constructed bag, but slimmer than I expected. Also, if you plan to hang a Garmin Varia off the back light strap, it will sag and aim pretty much down. You really need to be creative to fit much into the bag. I had to get a TPU tube and a smaller multi-tool, rearrange stuff a bit, but now have enough room for 700c TPU tube, multitool(with tubeless plugger), CO2 inflator, tire lever and Tyre Glider tool, and thin rubber gloves and paper towel . Anything more would require the large bag. It really locks into place under the seat. Varia needs to mount on the bike seat tube though, instead of the back of the bag.
