Like others have pointed out, this bag does very little to keep heavy rain out. I used to use old pamphlets as a kind of shield for the contents of my bag. The waterproof wrap doesn't enclose the bag and leaves rather a decent bit exposed. Rainwater will run down your back or coat and soak through the back. Or simply run off the top and down the back to the same end. Even if it did provide full coverage, I'm not a fan of needing to put on the cover or partially remove it to get at the contents of my bag. I really did like the camera pocket though, I must say. It is also quite a cramped bag. That's fine for some, but I like to carry a lot and have a bit roomier of a bag to do so. Also, sadly, not but three months into my Mission and I was already replacing broken shoulder strap pieces with carabiners. The rest of the bag seemed to hold up well, but the plastic pieces of the shoulder strap broke easily. A companion of mine had the same issue with his Taska.
I'm actually rather stunned as I was told that the designer of this bag went to the same mission as me: Iceland. Taska means "bag" in Icelandic. Yet, at least on Iceland, having a waterproof bag is an absolute must! We were always soaked through and I learned to stop caring, but I really wasn't too fond of handing out soaked and warped copies of The Book of Mormon. I was fond of the bag, but these things were a hinderance nearly every day before I got a different bag. For a less "wet" climate, I can recommend the bag if a small bag with good pockets is your thing. Bringing a few carabiners just in case couldn't hurt.
If you are a Missionary headed to Iceland, I would recommend at least a fairly water resistant bag. TimBuk2 is amazing and the stm Velo 2 is another good one. They're kinda difficult to find. If you find yourself having trouble with it while biking, shorten the strap. These wider bags don't tend to slide down as smaller ones do. Iceland actually got bikes when I had three transfers left, so there's much less walking in at least the two areas that now have bikes. The other two just ride busses everywhere. I also hear they finally got smartphones there, so that might be a factor in your bag choosing. Velo has a good pocket for that.