Brian, thank you for a very informative post. I'm a lurker who had the same question as the original poster, and it sounds like either board will work for most people. I guess the way to differentiate between the two would be to see which one has better support for a new user who isn't sure about how things should be wired together. I've looked at the open P-ROC forum and saw that newbies asked questions and got answers and they were able to build pinball machines, and while it's not public, I'd imagine that the FAST community has something similar on their Slack channel.

However, the tone of this thread makes me want to avoid both camps. With few exceptions, everyone seemed to hold a grudge against the other platform and the people who support it. It got really personal, really fast. I'm just looking to build a pinball machine, not join a cult. I think I'll put my purchase on hold for a while. Linolium had a good suggestion about developing without hardware first, so maybe I'll do that and see which group becomes more mature by the time my game is ready.