I bought one too this summer because it felt so natural versus all of the other brands, including the Even-Rolls which is what I was biased toward when I scheduled the fitting. So far, so good, but in full candor I have only played two rounds with it. Also, I have not spent much time working on putting, but I plan to spend more time on it this winter.
I just sent back my 639mb-plus demo irons (6/9) and they were a pleasure to hit! The only reason I have not ordered a set is because I feel like I need to try a New Level 902 iron first since they are among the Most Wanted player irons here. (Why weren't the 639's part of the test?)