The Dirty Little Scrubber hangs on the lower chain and a hook bar swings up behind the jockey wheel so when you back pedal the cranks the cleaner stays in place. The fact that you don't have to hold the cleaner with one hand brings 3 main advantages:
1) It finds its own position of least resistance so you don't get annoying chain suck when back pedalling the cranks - this is assuming that you have it in a gear that back pedals freely in the first place!? With hand held cleaners it is all too easy to twist or tilt the cleaner which inhibits the free movement of the chain through the cleaner.
2) You can use one hand to the hold the bike up and the other hand to turn the crank so you don't need a work stand to hold the bike steady.