I received my Pinstadium today and while I have no affiliation with the company, my feeling is that It may be the single greatest mod available (at least for a great many machines that aren't considered well lit - I.e. Non-recent machines)
I installed it on my Addams Family, which has full LED's but is still probably a fairly dark game. But there are quite a few games I play on location that are much darker, especially Indiana Jones, which I can barely see.
It has also significantly reduced glare coming from outside the machine (including DMD glare). However fingerprints and scratches on the glass do show up significantly more as well)
I've looked at the benefits of invisiglass on location, and I have a color DMD, but in comparison, those two significantly beneficial mods, in my mind would have to be ranked after Pinstadium in order of benefit to the machine and game play.
I've never heard Pinsound in person (only online) or upgraded speakers, so I can't comment on them, but I think I'd have to rank them behind Pinstadium in order of necessity. (And that's coming from someone's who's main hobby is high end audio)
I've attached a before and 2 after pics of my machine (one warm and the other with bluish light just to show its versatility) I tried to control for exposure as best I could, but they are only iPhone6 shots and don't really do justice to how much of an improvement Pinstadium makes.
Please feel free to post your thoughts on your most beneficial mod.
Other thoughts - the app is very well written since the owner's other profession is as an app coder. Customer service is great and responsive to problems.
My only negative is that the flasher option - while it looks amazing is perhaps a bit strong, possibly depending on how high you set the GI lighting on the app. But it can be disconnected if it proves too strong.
The GI option is highly recommended since it dims (or completely shuts off) in synch with the game's main GI lighting. It is extremely dramatic, and has brought my Addams Family to a new level, and I think may possibly even improve scores since the ball is easier to see.