1.About external anttenna suggestion
2.Most of feasycom bluetooth module which with on board PCB antenna ,also support external antenna.
If you already got an bluetooth module with PCB antenna ,such as FSC-BT909 same as the image of left side ,do not worry ,you can just change the resistance distance ,make it sidewards ,then it can work with external antenna (Refer image below ).
3.Some of feasycom bluetooth module already has on board antenna version ,and external antenna version .Such as FSC-BT909 ,FSC-BT616,FSC-BT836 .
So you can confirm this with feasycom sales before place an order .