Shares of 3D Systems (NYSE:DDD) and Stratasys (NASDAQ:SSYS) popped today on news that Citigroup analyst Kenneth Wong initiated coverage of these two stocks with a buy recommendation. In this video, Motley Fool industrials analyst Blake Bos tells investors why analyst recommendations may not be a very sound reason to invest and takes a look instead at several things 3-D printing investors need to be watching with these two companies' fundamentals.