The Diablo II is one of the cheaper helmets here and it's fair to say that you can tell. You only get three front vents and two very small rear ports, which immediately reduces cooling airflow. There are more across the top though, so it's not a total sweat bucket.
The moulded peak is non adjustable but it doesn't get in the way of the front vents and works fine for keeping the weather out of your eyes. Like the more expensive Mustang , the shell comes in several sizes, but the dial adjustable cradle sits very high on the occipital lobe (sticky out bit of the skull) and tends to slip up and off rather than stabilising the lid like lower cradles. The replaceable pads are low profile though - which helps reduce wobble - and the lid is covered by Apex's excellent free crash replacement scheme.