I asked pretty much the same question about the high speed overlay (they have been on ebay for like 2 years).
Didn't get a whole lot of feedback on the topic.
Some of the responders (or posts I found in searches, can't remember) suggest you have to pull out the playfield remove everything including the wiring, lights etc.., sand the original playfield down then install the overlay and clear it. Sounds like a really lot of work.
While I don't shy away from labor, might be too labor intensive for me with other more important projects to work on.

I was curious as to if you sell the machine, do you get the overlay money back in value.
Let's just say I have a $1000 high speed, is it worth $1200 with an overlay?
Do people care if a pin has an overlay?

I'm not in it to make money, i'm more about losing the least as possible these days.