May need to apply when very warm for better results
I purchased Giotto, GGI, and Hoodman screen protectors because I wanted to get all 3 and see which worked best.
Giotto includes 3 protectors, a nice cleaning cloth, and an ineffective cardboard squeegee to apply the protector. The big problem with the Giottos was trying to remove air bubbles from beneath the protector. While that was mostly possible with the GGI and Hoodman, it simply was not possible to get a good adhesion and remove air bubbles.
The Giottos was the most expensive per protector price - so I expected the best quality / ease of use - but this was not the case.
The Hoodman was probably my first choice. It seemed to have the best adhesion and went on fairly well with minimum bubbles. They include 12 protectors and a useful plastic squeegee. They do not include any cleaning cloth.
The GGI was also good. Included a plastic squeege card, 1 wet wipe, one dry wipe to clean the screen. They do have lines on each protector so it is a bit easier to cut the protector to size. Just don't use their black corner line - instead - start measuring from one of the pre-cut factory corners - that way you know you will end up with 2 factory cut - straight edges (which is better)
Either Hoodman or GGI can be effective, but I'd suggest passing on Giottos - it just doesn't work.
Done on a Casio EX-Z750