The TWO treatment option is an excellent choice:

If correcting a moderate number of conditions
When treatment required more than 24 steps, but less than 48 steps
When correcting moderate crowding/spacing
For overbite, overjet and moderate crossbite corrections
Fo mild-moderate correction of vertical discrepancies
One rate for up to 48 sets of aligners + two revisions and two sets of retainers
Up to two years of treatment