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 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.
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.