Just tested, definitely working.
The default state (engine off) is both DISAs open.
At idle, both DISAs are closed
At c. 2850 rpm, DISA2 opens
At c. 3800 rpm, DISA1 opens (i.e. both open)
Hence, three stage intake.
This is surprising, as it suggests the gains from DISA2 are in the mid range.