This top tube bag is very well made had very light. I bought a regular (small) size for use on shorter top tube dropbar bikes, so it doesn't get in the way too much when stopping and standing over the bike. It has enough room for a regular size iphone 6 (definitely not long enough for the PLUS ones), a wallet, and maybe two energy bars. The main issue I have is that the bottom strap interferes with the same brand frame bags I have... I have three Apidura Backcountry frame bags, one full frame in small size, two half frame ones in small and medium, and they ALL have the same issue... Maybe it won't have the same issue with the extended (long) version of the top tube bag, or if your frame bag allows you to move around the top straps. By the way, Apidura's Expedition line frame bags do allow different positions for the top straps, but I tend to go with the Backcountry line for the light weight.
I use this on my commuter bike to hold glasses, keys, and phone. I got the extended size because the other smaller one does not hold that much. This is long enough for a glasses case. I've used it in the rain and it kept stuff dry. The zipper is self-sealing. Perhaps in a really long rain ride things might get moist, but you can always use a ziplock inside.
This is the second one I've purchased. As I stated above, the top tube pack is light, well made, and stylish. It functions very well at the other end of the top tube fastened to the seat post. The only consideration to be aware of is if there is not much space between the headset and the stem you may have a hard time attaching the front strap as it is wide and positioned in the center.
This top tube bag looks great and works great. I love being able to eat snacks by just unzipping the bag and reaching down. That being said, after just 2 rides the fabric that is against the stem has started to fray, which makes me question its durability. There should be an extra patch in this weak spot to help protect the bag like there is on the saddle bag. I ended up buying gear repair tape to put in this area to keep from further abrasions. Hope it helps.