If you are on your own, the general rule established by a British university study some years back is that despite marketing claims for ramming air through and sucking air out, the basic principle prevails that the larger the front vents, the cooler the helmet. Cooling can be enhanced on almost any helmet by careful placement of fitting pads to permit air channels around the sides. Many riders find that they need a sweat band to keep their eyes clear, and that most helmets do not have adequate sweat control. That forces you to use a separate cloth sweatband, which wraps entirely around the head and is much hotter. The advantage is that in winter you just swap the sweatband for an ear band without changing the fit.
Style is as individual a choice as it is with any piece of clothing.
Just steer clear of the most extreme gimmicks. And that aero tail sticking out the back might snag in a crash. But the style appeals, so if that's what turns you on, buy it. For more on ventilation, check out our page on helmet cooling . In a crash you want an interface with the road that is smooth, hard, round and slick.