After years of riding with a traditional camelbak I started leaving it at home on shorter rides, and now I like riding that way so much that I'll do what I can to take no pack on pretty much any length ride. This little guy is a big help in making that possible, and it's not every day you can find a bike part that changes your experience so much for so little money!! It's a pretty basic item, but it works well and very securely holds a tube, two C02s, tire lever, and mutli-tool.
If your'e debating between this or just taping/strapping a tube to your frame, I highly recommend going for this. Being able to easily access and re-attach your stuff is much more convenient. I used to have my stuff strapped to my frame with a voile ski strap. That worked really well, except it was a bit of a pain to take off and put back together so I found myself mooching tools from buddies to avoid having to mess with it. This bag makes it easy to access your own tools whenever you need them.
I use the frame bag to hold a 650b tube, CO2 cartridges (2), and 1 tire iron. Fits my oversize Foes downtube and holds tight. 650b fits tight, so no movement, very secure on the frame, not sure how great a 29er tube fit would be though.