I can. The MPU uses a MC34064 to make the reset decision based on the 5v supply. The MC34064 has kind of a wide trigger range for dropping voltages (spec'ed to 4.5 min, 4.7v max, 4.59 typical). The Pro Daughterboard uses a Maxim Integrated's Max835 using the data sheet's recommended circuitry to target 4.7 as the trip voltage - so near the top of the MC34064 range. It has a min/typ/max trigger spec as well and the resistor circuitry will broaden that chip's range in the Daughterboard implementation, but it is not as wide as the MC34064.
So why would you never see red? Could be several reasons or a combination of reasons... Some already touched upon (or around) in the recent discussion...
1. Removing the MPU from the 5 volt circuitry does help stabilize it. As discussed in the technical details on my website (http://www.kahr.us/index2.html), the 5v does not fail linearly (when it exceeds a plateau of power delivery, output drops rapidly), so reducing the load (big load, small load, whatever) can keep the supply from reaching the plateau. So it is good news if you never see red because it indicates installing the Daughterboard has stabilized your supply. On my infamous Party Zone, it typically takes 50 to 60 minutes of gameplay for a Pro to detect a reset condition and the machine barely boots without a Daughterboard. As one might expect, reset is typically detected during an exciting multi-ball event. I consider that sufficiently stable to do no additional work on my PDB... and I really like having that increased understanding provided by the monitoring.
2. My Daughterboard monitors the 5v line at a different point than the MPU monitor point. The 5v line enters through a header, pass through an inductor, past some capacitors, and probably some other junk before reaching the MC34064. The Daughterboard monitors BEFORE the J210 header so losses downstream of that are not seen by the Daughterboard (and appropriately so, b/c they are no longer in the PDB 5v circuitry). So, your MPU may be "lossy" on the path to the MC34064, but it doesn't matter because you are delivering solid clean power to it that easily overcomes any such "lossieness". Sorry for making up words but hopefully that makes sense...
3. Thinking about the spec's above, you could happen to have a high-threshold MC34064 that was triggering resets and a Daughterboard that senses below your MPU's threshold. Seems unlikely but it could_ be.
Also remember the Pro's latched output indicators are reset by rebooting the machine. So you shouldn't power up the machine and expect to see whether you've had a reset since you last looked... it's only since you turned the machine on. Turn it on, play a few (or a lot) of games, and then look. Do this every month or two (or three... whatever) and you will have a feel for how your power supply is performing over time.
I hope that helps explain some of what's happening and why the Pro is a good thing to get... if you are actually going to look at it. If you're pretty confident you'll never look then by all means just get the Classic. If it helps you decide, about 30% of the Daughterboards I ship are the Pro version.
-visit http://www.kahr.us to get my daughterboard that helps fix WPC resets or for my Pinball 2000 H+V video sync combiner kit