This is how I feel about makeup tools especially brushes. If you use it all the time and can't live without it, it becomes a good buy no matter the cost. If you spend that money and don't use the brush often then it becomes a dud. So far, F has been a very useful brush for me and I use this everyday together with my L. So definitely not a dud.
I would say that is you are working to build up your brush collection, splurge on some good face brushes and skimp on the eye shadow brushes. Work up the the eye brushes later on.