A lot of cruiser/classic bike riders don't wear full face helmets. I was one; my first helmet is/was what's called a 3/4th style where eyebrows to jaw is open to the road. It afford great visibility, feels very free, and I'll still wear it on a low speed excursion around town or on a back road.
But highway riding is a different beast. The above picture is the same model full-face helmet I wear, taken from a
Reddit thread thanking the manufacturer. The what-if-you-crash reasoning is sound enough and needs no re-hash here, but the secondary benefits have their own immediate value and importance. Full face helmets cut the wind much better than open helmets; your neck will thank you after long rides. They can be cooler since they have more directed vents and air channels or warmer if you close those vents up. they keep bugs and road grit from getting to your eyes/face far better than any bandanna/sunglasses combination ever will.
Before I got the
ICON Alliance, I had a different brand full-face helmet for my commute. On the ride to work one day, the visor on my helmet came free on one side. I was able to secure it with duct tape, it it's still an unnerving thing to happen at 70 mph. While the duct tape would hold for a few days, I'd decided to shop around for a better helmet.
Safety and design details are what drew me to the Alliance; price is what made me choose it. They're both mediums, but the Icon fits more snugly. The visor mechanism feels more secure and it has a steel retaining pin to lock it in the down position. It's $40 more expensive, but I feel like I'm getting more than $40 worth of improved design features and functionality. This is what's good for me and my head, but there's no replacement for trying on helmets in-person. Heads vary in their shape and proportion and it's safer to have a cheaper helmet that fits than an expensive one that doesn't.