It is like a tradition to have promotional stuff come up before and after a good movie is released. Most of the toys, accessories, and other promotional stuff are great, as long as they are promoting the same idea. Promotional stuff are useful only in the showcase areas of shops and malls promoting them.
The new Darth Vader backpack, lets you carry this menacing character of Star Wars on your back, carry all your everyday stuff in it, and is very handy, probably a good buy for Star Wars, die hard fans. Besides that, it does not do much good to keep the ‘effect’ of the Darth Vader alive, except for kids maybe, who would like to impersonate the Vader.