Functional, but flawed – I bought the Java Sok because I often buy Venti (24 ounce) drinks from Starbucks. I love how it insulates the cup. My complaint, however, is the fit. The cup doesn’t go all the way down to the bottom of the Java Sok. This causes the cup to be unsteady, even when placed on a level surface. I often feel as though it’s best to lean the cup up against something stable to ensure that it doesn’t tip over. For that reason, this is not a five star product in my opinion.