This was a popular choice for many teams, including my team in the 2014 season. As Ether mentioned, the design may seem simple at first, but getting the puncher built in order to work exactly as you want is a challenge.
Here are a couple
puncher test shots from our 2014 build season video blooper reel. We labored for hours to get a linear launcher that shot balls from above the assembly rather than from in front of the assembly.
Here it is working from the same video.
It was so difficult to get this working that we had almost scrapped the idea altogether.