Is there any particular reason why you haven't used the flap? If its that you prefer using your GST, then you should probably sell the flap.
However as has been mentioned here, quality control seems to be getting slacker, you might find if you are to repurchase a flap later the quality is not as good, but with an inflated price tag.
If you use the GST on a regular basis, maybe for a week you should try using your flap, and see how you feel about it afterwards!