Just for accuracy - these used to be made from Lexan - these new 0.5 mm ones are made from PET-G. I can sure vouch for the durability of the old Lexan protectors (had them on some of my machines for years - yes, nice shiny balls always). I'm thinking these PET-G products will have similar durability, but only time will tell. I only wish they made them for all of my older machines.

Yes (Met). It eliminates playfield dimples and totally protects magnets. A little more difficult to install than on an old EM, but I think it's worth it.

Yes, and I even have the thicker Lexan (.75 mm) type. Sparky magnet looks like it did on Day 1.

Put spacers (washers) under the sling posts to elevate the kicking rubbers the same height as the thickness of the protector.

Raise the height of the spinners .020" by putting spacers under the posts.

The inline drops would originally hang up the ball on my Metallica, but I adjusted them level with the protector. No hangups since.

I can think of two:
1. They eliminate playfield dimpling.
2. They eliminate magnet wear (i.e., Met Sparky magnet).

...or install a playfield protector from the beginning and never was or will be relevant.

Wrong. I've played machines both with and without, and there's really not much difference in my opinion - both are equally enjoyable.

They are correct, you are correct, and I am correct.

Nice Power Play. It looks like they have changed the design/fit around the rollover buttons. They used to have a large clearance around them and a triangular cutout below them to prevent the ball from getting stuck in them. The trouble was that it really affected ball trajectory. How well do the rollovers work with this new design with respect to the ball changing direction or getting hung up? Did you raise the rollover inserts to the same level as the protector?

I would imagine a fast moving ball could skip over the star rollover, and therefore not deflect the switch enough to score points. Have you noticed anything like that happening?

The star rollovers were the only knock I had against these protectors - just curious to see if they overcame problems associated with them. Maybe the 0.010" reduction in thickness was the key to eliminating these problems.

Punch is the way to go for no raised lip or deformity around the hole (see this thread from 2 years ago). Keep the punches sharpened. For large holes (such as clearance for pop bumper skirts), an adjustable fly cutter at slow speed works well.
https://pinside.com/pinball/forum/topic/polycarbonate-playfield-protectors-suck-got-the-perfect-fix/page/2#post-3242505