I agree with what you just shared. I tried coating the SP with cheap ceramic coating from lazada.
Works quite well. Not sure how long the coat will last. So being an OCD, I usually change my Glass every 6 months. So i buy the cheapest generic i can find. . . ways of a cheapo . . . lol
Though I am cheapskate I have never tried apply SP myself.
I will let the mobile shop to help me with that.
I do thought of regularly replacing the SP but the amount of time and labor cost associated with the replacement deters me. 