I got one here. The only real issue I've had is that it doesn't work as well as it could with the first type of sound board like was used in Solar Ride; It took some parameter tuning to get the tunes to sound remotely right. It's generally better to use the "sound file" functionality. I would also indicate that it isn't an instant boot process; I'd recommend just using a Pi3 on it just to reduce the boot time. It can use ROM files like you'd use with MAME/Visual Pinball, so it's exactly the original rules, complete with the limited settings. You can access the original diagnostics/memory menu, but you can also, holding the button longer, access a more advanced diagnostics screen accessible via ad-hoc wifi, which means you can test individual lights, switches and coils via a tablet interface, which has been really handy; I did pop bumper adjustments by using the diagnostics to engage the game-over coil so that I could fire the pops without entering the original test mode, and then disengage it again to adjust the switches again.

The real shining feature of the kit over the other replacements is the ability to configure rules with Mission Pinball Framework, although I have had issues with a form of "lag", where it would get gradually slower in responding to switch hits. It doesn't affect single player games currently, but it can affect multiplayer games, and it can be measured in seconds at the end of the game. It's also a "from scratch" sort of deal, I think I'm the first one who got a "flips and plays" config more or less finished, and I do believe that Ralf is now including it with the main distribution as an example.

Technically the Pi Zero does run fast enough, but it's not pleasant. It works perfectly well if you're just running the ROM file and not bothering with MPF. If you're using MPF, then a Pi3 is what you want to be running, and it's still cheaper than stuffing a real computer in there. At some point, I'll test using the computer I was using for config development (running the Pi in 'slave' mode), and see how well that runs a full game.

Do note that even with all that, you still have to deal with the limitations of System 1... the lack of computer control of the pop bumpers, the lack of being able to tell what the flipper buttons are doing, the real difficulty of trying to add a high score name feature (I figured out how to override the "enter initials" feature so that it just records the high scores), and getting around those by rewiring, you might as well rewire the whole machine for FAST or PROC.

Yeah, header extensions are necessary. If I do another LISY, I'll use the extended plugin instead so that it can take a Pi3 without adaptation.

I used a wireless dongle on mine, actually (also original Zero, not W), and it worked fine. You just need to buy a "USB On The Go" hub to connect it.

I think there were some issues with wireless at one point. I found it worked better just doing the adhoc networking and pointing the tablet wireless at it as if it were a network.

Doing the HDMI won't get you much... all you'll see is a command prompt login, it doesn't provide a console on the screen to monitor how things are running, it's basically meant to run "headless" or attached to an external computer like any other USB device, which is how I developed an MPF config for Solar Ride.