I used the Studio Live 24.4.2 for a weekend a few months ago. I didn't need to crack open the manual... everything worked as if it was an analog mixer. You do need to allow yourself some time (a few hours) to get familiar with selecting a channel and then adjusting it. I gave a demo to a few music teacher friends and they got the concept really quickly. The same weekend, I used it for a gig where I supplied the sound for a New York musician. They commented on how nice everything sounded. I could give the musicians what they needed within a short amount of time.
Presonus just released a smaller mixer called the 16.0.2...
http://www.presonus.com/products/Detail.aspx?ProductId=62If you need the channels, go with the 24.4.2. If you need 16 mic pre amps, go with the 16.4.2. If you want the smaller package and don't need the 4 buses, go with the 16.0.2. All of the units can use a iPad to control the features. The biggest benefit for the small unit is MIDI. You can preset your effect changes via MIDI.