These are really good! I bought two of the 14mm versions, one for me and one for my brother. The bowl looks pretty classy and has a nice solid weight and feel, a bit like a crystal decanter stopper. The cut glass picks up the light reflecting and refracting it aesthetically.
Not only is the bowl deep it draws very cool and smooth improving whatever size bong it finds itself in (tested in a 20cm and 40cm bong so far).