Well last time I installed a hori, I was lazy and didn't use that method. I only got one bubble that I couldn't get out, and I managed to get a fingernail under there and flick the dirt particle out a few weeks ago. It looks as good as my first switch hori which I forgot if I installed it in the bathroom or not, probably not though.
So in that case, I recommend making sure you take a real good look at the screen after you clean it making sure there's no dust particle on it and then install the screen protector according to its included instructions and you should be fine. If it is really dirty you might need some windex, don't use generic windex use the real thing.