Heads boot line up (as with most companys) can be broken down into three catagories with multiple 'levels' in each catagory so there is crossover.
Comfort= recreational boxy fit, fluffy liner, simple, cheap, designed for someone who will never ski more than 10 days a year and won't pack out the boot. Head EZON line.
Comfort/Performance= more anatomical fit than comfort boot, denser liner that won't pack out as quick as fluffy liner. These are usually feature packed boots. Think walk/ski, flex adjustment, etc. Tese lines usually range from lower int. to advanced/ expert. Head Edge series.
High Performance/Race= Very dense thin liner, less features than comfort/Performance. There shouldn't be anything goofy like a 'walk' mode. Should have micro adjust metal buckles and maybe cuff alignment and nothing else. Fit is everything the liner isn't used to make a boot comfy in the store. Head S series and RD/RS.