I bought the Personal Cup Adapter about 2 months ago. Love this product. It makes very smooth smoothies. It may get clogged if your ingredients are to big. I make sure to cut into small pieces, not to overfill, and add adequate amount of water - and  I get the best smoothies ever!
One drawback is that things may get messy if I have big pieces, or not enough water, and have to open to correct after I had started blending. Also I wish it could be used upright and not upside down. Washing the adapter is tricky but not a deal breaker.