I have written about the Fjällräven Sling Kånken before, here.
I bought one when we were in Tenerife. We were walking so much each day and I was looking for something smaller than my Longchamp Le Pliage.
I really like almost everything about it. It is light, water resistant, durable, easy to wear, and fits a paperback book perfectly in its back pocket.
The only thing I am not a fan of is the tiny size of the front zipped pocket. You can fit coins, hairclips, travel card etc in it, but it is so hard to get them in and out. Ultimately I don’t use it.