Hi Mighty Mom!
I was planning on creating a hub around this very same topic, just haven't gotten around to it yet :)
I like them because of the personalized approach to it. They pick out various shoes for you each month that match your fashion tastes. Its pretty fun and you can be assured that you always have this seasons hottest styles.
But the best part is the price... They are inexpensive shoes... For Shoedazzle and JustFab you pay 40 bucks a pair and they are more like 80-100 dollar quality shoes.
Give it a try if you havent yet!