I must say that I'm a little bit unhappy that even now there are no official (or unofficial?) stats on the effectiveness of the booster cell.
If you're getting it purely for how it looks, I guess you're in the safe boat where its looking good. But if you're getting it to improve cooling or decrease noise (maybe most peoples expectation?) you're really stabbing in the dark whether this thing actually functions as intended. As Alex says, the effects are "subtle", which I don't think is a good sign, and I've always had my minor doubt whether a fan blowing in/out on the side of the GPU/PSU area is actually going to achieve much apart from adding fan noise.
If I had to hedge my bets, I think not knowing how well it performs is going to be beneficial for the sales of the booster cell and that doesn't make me feel so good about this potentially strategic move. If some people who already have their cases can do the testing with noise normalized thermals, that would be greatly valuable.