Since I have over 185K km, and still on stock ceramic type plugs, I will be replacing them regardless. At this stage the recommendation is to use the Bosch 5v due to better performance, and no flashing should be required.
The 4 Bosch plugs (0250402003) cost me $66 delivered from the UK.
https://www.idparts.com/glow-plug-5v...rd-p-2858.html