First I'll say that the quality of glass is top-notch. For that reason alone, I'd consider buying more products from Grav.
Unfortunately, there are some design and QC issues that make this piece difficult to use, if not unusable.
-QC Issue: the top of the bowl is significantly higher on one side than it is on the other. This makes packing a full bowl difficult, as one side is tucked safely inside the glass bowl while the other side of the material is exposed and hangs over the edge.
-Design Issue 1: the Upline rings are supposed to help aid diffusion in the chamber, but in my experience the regular Grav bubblers (which don't have the Upline rings) produce much smoother, cooler hits. Also, the downstem on this piece is diffused with two circular holes near the bottom tip of the downstem. The regular Grav bubbler, on the other hand, uses an "X" pattern diffuser on the downstem, which creates much smoother suction in my experience.
-Design Issue 2: the Upline rings near the mouthpiece look pretty (and they probably reinforce the glass in that area, too), and they probably do prevent backsplash from happening a little bit. That said, if/when backsplash does occur -- or if you've gotten the rings wet while cleaning the piece -- water gets trapped on the rings and it's nearly impossible to getting all of it out. Since I drain the bubbler and use fresh water every time I smoke a bowl, this means that the fine droplets of water that were stuck on the rings constantly spray…