I've only used the adapter a few times at this point but all in all I think I'll be happy with it for the most part.  I've been using it to make two different smoothies each morning for my wife and myself.  I've noticed that the smoothie mix does tend to stick up in the topside of the glass while mixing (actually bottom of the glass because it's upside down) but generally a tap or two while turned off has worked fine for me.  After use I can provide a quick rinse to the adapter and I'm done and I feel there is less waste by using the personal cups....