It has enough inputs to actually record drums if you need to as well as two effects sends among other additions which I think are well worth the extra investment upfront. I would be seriously trying to stretch to the L-20 though if possible. So many features and so much versatility. The Zoom Livetrak series are worth considering I think.
The main disadvantages are that you pay more for the mixer, the mixers tend to have higher latency and you miss out on the better drivers available for a selected subset of the best audio interfaces.
So they do have their place, particularly if you have your gear set up and permanently hooked up to rehearse, write or jam without wanting to fire up the DAW. The mixers also sidestep the issues that comes from trying to buy and connect a mixer to a multi-channel interface if you end up wanting to - namely the search for a mixer with enough channel inserts. In other words, you can monitor and mix stuff without turning the computer on if you like. The main real benefit of a USB multitracking mixer compared to an interface with an equivalent number of inputs is that you can use the mixer with or without the DAW.