It must of course be VERY careful and operate with great caution, the slightest speck of dust and the film is to throw, because it is impossible to get a good result after taking off for the pick.
The fact that there is 3 gives leeway, so if you are not used take time to train with the first film, and do not seek perfection, if you draw with 2 or 3 small bubbles better be satisfied with that, you better have 2 air bubbles on the screen as two stripes.
I remain reticent as to the price, I find that 8 for a piece of plastic that is still too much, but it remains a personal opinion.