Trek's 30 Year disruption (WaveCel Helmets)

How’s the coverage on the back of the XXX vs the Trek MTB helmets?

I need an aero helmet for Leadville, but I’d also like to upgrade my existing MTB helmet.

Ideally, I could just use the same helmet for road and MTB. If the XXX won’t be great for MTB, I’ll probably get the Ballista for road/Leadville, and use the $100 saved vs the XXX towards a MTB helmet.