Every so often one of Scubapro's regulator's enters the "LEGENDARY" category.  The old MK10-G250was a work horse and set the bar back in the early 90's.  The Air 2 revolutionized the octopus.  The current version of the MK20-S600 has entered that realm.  Once it got there, Scubapro started having fun.  They offered a Titanium version, a Tech Black version, a GOLD 50th Anniversary version and the latest, the Deep Blue.