I've read lots of articles as well as reviewed quite a few prepaid plans over the past 10 years. With any prepaid plan, if the purchaser does not understand what he is buying, then it is bad for him period.
Though I have great respect for Joe and what he's done here, I don't view his position on things as the gospel. I've had my disagreements in his 529 rankings over the years, and the article you point to is very one-sided.
The focus of the article was solely on those prepaid tuition plans which charge premiums, in essence to make his point. What was left out of the article, were the MA U.Plan and Independent 529 plan, both of which are open to residents of any state, and have absolutely no premium on tuition. In fact, up until the current purchasing period, the Independent 529 required all member schools to offer a minimum of 1/2% per year discount to participants.
Again, the article is slanted to make a point and justify the statement "Prepaid tuition plans are often thought of, or even marketed as, "buying future tuition at today's prices." With regard to the Florida Prepaid College Plan, that is not the case at all. In fact, you're buying future tuition -- but at very inflated prices."
As time goes on, and tuition rate increases continue to eclipse inflation by a healthy margin, prepaid plans offer the ability to lock in future tuition rates today. Many of the plans are no longer the bargain they were a few years back, however, that doesn't take away from the fact that there are still those where you can buy future tuition at todays rates with no markup or fees.