I had to ditch the bag I have carried for years under the back of my saddle (that carried spare tube, CO2, tool, etc). I decided to give that under-seat space to a light-&-radar unit that attaches to the seat post. (Love the radar, by the way. Nice addition to safety.) I was reluctant to use this bag because I just didn't like the idea of positioning a bag on my top tube. But it has worked out well. It carries my stuff with room available for my wallet, which I hadn't been taking on rides before. I bought a different one first but it turned out not to have the capacity I wanted. The Topeak bag is completely out of the way and doesn't come in contact with my legs while pedaling. Holds its position well and seems to be quite well made. Again, I don't love the look of a top tube bag but I'm over that; I'm happy with my choice and I'd recommend the bag.
Bag shifts to one side or the other while I'm riding. With three straps, I expected it to be more stable on the top bar. Sides are very stiff, so barely holds one tube, small hex set, CO2 injector and cartridge, small tube repair kit and a couple of tire removers. OK value for the price.
I shopped around for a top tube bag that had sides that hold shape, one that doesn't interfere with my knees, looks good on the bike (always important, right?), and has room for 2 CO2 cartridges + head unit, spare tube (700x30) small tool set, ID and cash/credit. It's packed full and holds all of this. The materials are high quality including the zipper. This checks all the boxes for me and just plain works!
This is a really nice, high quality, top tube bag.
The straps are nice and large so that when you secure it, it sits firmly on the bike. You can also, easily, take it on and off the bike because of the nice Velcro straps. If you ever have a cheap bag you'll know why good quality is important.
The bag itself can fit a few items as one would expect.
If you leave the bag unzipped the bag stays fairly well closed, so that even though it's not as secure as being zipped shut, you don't necessarily have to worry about things just bouncing out.
I purchased this to store my essentials during the Dirty Kanza 200 and Michigan Coast 2 Coast and I'm very satisfied with how the bag held up. I expect that I will have this bag for a long time.
Nice pack for getting your phone, extra bars, etc off your back. Generally fits, a cell phone, two Clif bars, small tube of sunblock (and a little room for keys). Secures snug to the frame with velco, slips under cables well too.