Lamshaw Universal Round Watch Screen Protector, [6 Pack] Full Coverage TPU Clear Film Anti-Scratch, Anti-Fingerprint, Bubble Free (29mm Diameter)

There are plastic screen protectors for watch crystals if really worried about scratches such as.. https://www.amazon.com/Lamshaw-Universal-Protector-Anti-Scratch-Anti-Fingerprint/dp/B0C27TLV4D Alternatively, Polywatch works very well on acrylic crystals to get rid of scratches.