I agree the open ear design becomes useless when you find yourself cranking them to drown out outside noises. Like someone else said, they are good for long boring climbs(MTB and especially gravel grinding).I use aftershox when running. They do sometimes drop my pixel connection for no obvious reason, but it's rare.
The open ear design is a nice idea, but IMO whether it makes me more aware of traffic noise etc. remains entirely dependent on how loud I crank them.
I don't wear them when riding unless I'm expecting a call. Regardless of which headphones I've tried, all I get on the bike is wind noise unless I have them deafeningly loud.... which is why I've never really understood EITHER SIDE of the bicycle headphone debate in the first place, but that's another can of worms.
I remember seeing flaps that velcro to helmet straps to block wind noises. They were aimed at road cyclists who deal with it much more but I imagine they would work for MTB.