A quick lesson and why it's a better buy than the cheaper one -
The VOICE control - 6 different types of presets that emulate famous amps like a Vox, Marshall, Fender etc.
The ISF control gives a British or American tone to the amps.
The EFFECTS control and Buttons - quite a few to choose from and very easy to setup.
The headphone output is an emulated speaker out, I had my Blackstar going through a 3000 watt PA System and it sounded awesome.
That USB socket means you can attach it to your PC and use an editing software you can download for free.