I have the medium Fendi B in cream canvas with a black patent trim. The pic you've shown is the medium bag and it's fine for my day to day needs. It holds a large wallet, make up case, mobile, travelcard, keys and even a book. Access is a little tricky as you have to press the release clasp each time you want to get in which (for me) means taking it off your shoulder and balancing it on one hand whilst holding the flap open (which is quite heavy as it has all the 'hardware' on it!). Not much fun when you're in a fast moving queue for the card-readers in the tube station!
Having said that it is a lovely, good sized bag and surprisingly practical. I decided to invest because I believe it's going to become a classic but I know there are those that don't. If you are also considering a Chanel and you want longevity in your purchase and a bag that won't date you might be happier with that. I am a complete convert to the B Fendi bags though, they're fun-loving and cute which quite frankly is what you want on a dreary London morning! Let us know what you choose!
P.S. I might post some pics of said B bag if anyone's interested??