This appears to be a simple pouch capable of carrying some three pounds. In fact, it operates as a bag of holding capable of carrying up to 50 pounds of weight while having an encumbrance of only three pounds. Furthermore, the bag of vanishing may have its drawstrings tugged tightly once per day and it just disappears for six turns; the equivalent of a rope trick spell will operate on the bag (although it stays with its owner) and it also has detection resistance operating on it.
This bag is invaluable for smuggling, as should be obvious. The only problem is that each time the rope trick function is used there is a 5% chance that the contents vanish into the Ethereal Plane and the bag is empty when it is checked later.