Beyond and the 2nd Edition are both great buys - but in Beyond there are a few references to the 2nd Edition/original book that assumes you've already read it or have it to reference the various templates. The Simple Strength Template isn't in Beyond 5/3/1, but was basically replaced by the 5s progression which is. Also, Beyond has many more templates than the 2nd Edition, including the Beyond 5/3/1 Program.
Buy one, and when you get bored with it, but the other. And a new book is coming out soon - buy that one too.
I bought Beyond before I bought the 2nd Edition; you really can't go wrong with either. One thing is that the 2nd edition has some very basic templates in it, whereas Beyond gets rather creative and expands upon the original through Jim's revelations and personal experience. - my opinion as the reader, perhaps he has a much different perspective.