I have these in black and wore the heck out of them (they are actually 4 years old and look good).  If you are familiar with birks, you know that they take a lot to break in.  The sole starts out quite flat and as you wear it develops a slight curve.  I actually tripped on a sidewalk, being used to my more broken-in pair and fell to my knees.  Very embarrassing.

Also, your feet get used to gripping the toe bar with can ruin you for a lot of other shoes.  This feature allows you to wear them for hours without complaint.

You will get blisters along the top of your foot.  Break them in slowly.  They aren't for everybody, but I love mine.

The leather in this pair is particularly forgiving.  After I fell, I was able to spray the leather with a sealer and easily buff out the scratches.

It makes sense to invest in cork sealer for any birks.  They can really prolong the life of your sandals.  Since the footbed is suede leather, you will get foot prints on it, unavoidable.

So, this list is mostly cons, but there are a lot of positives in Birks.  Like not sweating or overheating.  Quality construction than can take a beating.  Simple designs, that while not fashionable, go with a lot of your closet.