I guess it depends on what you want it for/how you'll use it.
My DD is 11 months old and I just use a normal largeish handbag which I put a couple of nappies in the front pocket, a little snack box and her water bottle. I don't carry a lot of stuff for me - wallet, keys, sunnies, tissues, lipstick is about it. So that's all I take for most outings.
I have a change wallet in the car and will chuck that in the bottom of the Pram if going out for a long time. I also keep a spare set of clothes in the car for her. I have a baby chic Pram caddy thing which I keep a muslin wrap, hat, Pram clips in.
If we are going somewhere like someone's house, or a picnic then I have a big isoki nappy bag I got for $30 at a baby expo. In this I'll put her lunch bag, bag of toys, change wallet, jacket etc. For me it's way too big and bulky to use day to day.
The bag you're looking at looks about the size of the isoki bag I have. Even if you don't use it every day you probably will get use out of it later as bub grows and you need to take food, toys etc and useful as a beach bag, travel bag too.