'Karma Police', track 6 of OK Computer, is an exceptionally well-crafted song. Combine that and two other great songs, including 'A Reminder' (one of the best B-side tunes available from Radiohead), and you have yourself a worthy collectible item.
Take notice that I have used the phrase, 'worthy collectible item' instead of 'worthy purchase'. I say this to suggest that it is only worth buying if you are a dedicated Radiohead fan, looking to build a collection. However, a more 'worthy purchase' would be the "No Surprises/Running Away From Demons EP", as it includes the same two B-sides, plus three additional ones and one other OK Computer single.