I prefer the blinkie getting a seatstay mount over using the seatpost. Easier to have a seatbag attached without the light having to squeeze into the now crowded space.
Performance has the headlight/tail-light combo on sale for the Cateye lights, the EL500 in the front and the TL-LD170 for the rear. Does that rear light attach to the seatstays, or just to the seatpost??