The main differences between the eTrex and GPS12:

• The eTrex is about 2/3 the size and weight of the GPS12
• eTrex is simpler than the 12, has different menus. It has less navigational functions and less "doodad functions". It's likely the easiest to use GPS ever made.
• eTrex is rated at IPX-7 for waterproofness, same as the GPS12 (1-meter submersion for 30 minutes.)
• eTrex will hold ten saved tracklogs. GPS12 holds one tracklog. GPS12MAP holds ten tracklogs also.
• eTrex runs up to 22 hours on two AA batteries. GPS12 is bigger, but runs about 24 hours on four AA batteries.