I was replacing my glass back panel for the second time. And I read about the Pentalobe screwdrivers being good for a single use because they strip so easily. As I was reassembling, one of the screws seemed to be stripping, and when I looked at it with a magnifier, sure enough, it was. I stopped immediately, leaving both screws half out, and ordered the liberation kit, having to carry my phone in a case very gingerly until the kit arrived in two days.
Once I had the kit, I carefully removed the pentalobe screws. One I was able to remove with the pentalobe screw driver, the other needed pliers, so it was a good thing I'd stopped when I did and left it half out.
I hadn't noticed that the screws were replaced on one or another visit to the Apple store, or maybe they were original since my phone has been replaced.
If I had it to do again, I would order the kit immediately and replace the screws with the glass panel.
I was lucky. The half out screws could have been knocked, and broken the sink holes irreparably. I could have been in just a bit more of a hurry and stripped the screw, making it irreparable.
You might want to have a jewelry pliers available if you can only raise the screw a bit before the head strips out. That way, you can gently twist the screw out the rest of the way.