I've been running the original first edition 5/3/1 for about 11 months now, and I still love it. I bought the Beyond 5/3/1 book recently, and I'm getting ready to switch to that for my programming. After doing the original for almost a year, while I've seen amazing results, I'm excited to use the new stuff from Beyond. Beyond has a lot of extra assistance templates and quite a few challenges, but (for me) the biggest difference program-wise between the two books is the deload frequency. In the original, you deloaded after every cycle, or every 4th week. In the Beyond programs you run two full 5/3/1 cycles without a deload in between, and then you deload every 7th week. I don't own the 2nd edition book, so I don't know what the deloads in that were. The philosophy behind the training max is also a little different.
Personally, I wish I had gotten the Beyond book about 5 months ago, but it's really not a big deal. All the underlying principles are the same. The original program still works really well, but Beyond seems to be tweaked to be better. If a new book is coming soon, I will also get that one.