Misleading headline. It's an isolation experiment, and the six person team are not astronauts. Only in the loosest sense is it preparing anyone to go to Mars, or simulating life on Mars. It's also not even the longest to date.[1]
[1] "Other simulation experiments have taken place under the ocean off the Florida coast, in Antarctica and in Russia, where a 520-day Mars experiment was carried out in 2011."
You better just read the "The Martian" Andy Weir's book than sitting in a dome for a 6 month. And for what reason, Russians have already completed such kind of experiment in 2010-2011 and the length of experiment was more then 500 days https://en.wikipedia.org/wiki/MARS-500
Eight scientists lived in a closed biosphere to simulate what a potential colonization scenario might be like (among other things). The first experiment lasted 2 years, and encountered environmental issues, but also some psychological upsets - the crew split into two factions who became bitter enemies, among other things.
Looking at the pictures, this doesn't look like a sealed environment (which biosphere 2 was). The dome is made of fabric and there doesn't seem to be an airlock.
If it makes you feel better, if you're interested in helping get people to Mars and elsewhere in the solar system, there are almost certainly more productive uses of your time than camping in Hawaii for a year. :)
[1] "Other simulation experiments have taken place under the ocean off the Florida coast, in Antarctica and in Russia, where a 520-day Mars experiment was carried out in 2011."