For starters, it's lightweight at 7.5 grams, has dual microphones with "noise-canceling DSP and GSMA-certified HD Voice," provides outstanding battery life (7 hours of talk time) and is fairly affordable at $60.
I tried it out while walking the noisy streets of New York City and have been generally impressed with the audio quality -- and so, too, have the people I've called. The overall build quality isn't quite on the same level as Plantronics' Voyager Legend. But the headset is the half the weight and like the Marque 2, very comfortable to wear.
Finally, the Explorer 500 comes with a magnetic strap which can be connected onto a laptop bag, belt loop or whatever, and doubles as a USB charger. Alas, it doesn't have a built-in battery for recharging the headset on the go, but it could be cool if it did.
The Explorer 500 will come in white and black in North America. A gun-metal gray version will be available in Europe, where it will cost €59 and £49 in the UK. Absolutely no word yet on Australian pricing or accessibility.