Who are smartwatches like the Apple Watch and Android Wear really for?

Is the smartwatch the next big thing after the MP3 player, smartphone, tablet and phablet, or is it the 21st-century equivalent of the electric can opener?

Smart watches are attempting to break into the mainstream. The massive marketing machines of Apple, Google and Samsung are trying to push their appeal beyond geeks and early adopters and get everyone wondering whether there's a smartwatch for them.

Smartwatches have existed, in various incarnations, for 10 years or so. Last year saw Pebble launch the second iteration of its successful smartwatch; Samsung unveil its fourth, fifth and sixth smartwatches; and Google enter the game with Android Wear.

Related: Apple Watch review: beautiful hardware spoiled by complicated software