You can access your effects by having foot switches plugged into your amp?
Yep, it's pretty cool. There is a caveat.... Not sure how familiar you are with this stuff, so hope I'm not overexplaining.....
The interface is based around modeled presets. You can choose from 10 or 12 classic Fender amps, dozens of effects... you can really tweak it and get just the sound you want. You then save this preset, give it a name. There is room on the Mustang III for 100 presets. You can easily put them in any order you want.
The amp comes with a 2-button footswitch. There is also a 4-button switch for $50-60 US. You can plug both in and have six switches in all. They are compact and sturdy.
You can tell the amp to use the switches in a variety of ways. The simplest use is just to toggle up and down through the presets once you have them in order.
To access the effects with the switch, all you have to do is set up the given preset with the effect you want. It doesn't even have to be 'turned on'. You can then tell the amp to let the footswitch turn the effect on and off. Does that make sense? You don't have unlimited access to all three dozen effects - they have to be used on the given preset and you are limited by the number of switches.... does that make sense?
The ideal set up is to have both switches ( the 2 and 4 button) and use the two button switch for up/down toggling. Then the four button switch can do everything else.... it has a button that allows you to easily change between uses for the four buttons - you can quickly go from using it to turn effects off and on to having quick access to you favorite three presets. There are several different options for set up, lots of flexibility.
I'm certainly no expert with regards to this stuff - this is the equipment I have and it works well. Several companies make good sounding modelling amps, but the Mustangs seem to have the most versatility and ease of use.... the most bang for the buck.
One other cool thing - you can USB into your computer and make all of your preset adjustments there so you don't have to use the knobs and tiny screen on the amp - although they work pretty easily in a pinch. You can also plug in an aux audio source with an 1/8in jack - I play to backing tracks with my iPod, plug in my metronome for running scales.... I've only had the amp a few weeks, but it's pretty great. A guy I play with has an old Fender Twin Reverb tube amp (one of the amps modelled for the Mustang) for his Rhodes Piano and the Mustang sounds pretty dang good next to it.....
Sorry to be so long winded.... probably more than you wanted to know.....