If you know anything about kid carrier backpacks you'll know that they aren't cheap!!  These look to be in the $280 range right now new.
It was hard to tell from anything on the pack whether this was the Kid Comfort I,II or III but they designs seem fairly similar.  
From personal experience we can vouch that you can use this pack with taller children as there aren't "stirrups" or anything for them to catch their legs on.  There aren't really kid carriers that are as comfortable as regular backpacks because of how and where the weight has to ride, but this one isn't bad.  
There is a hole in the rain fly and it looks like one of the little rubber pieces on the bottom of the stand is missing but other than that it looks to be in good shape.  See pics for more info.