iVol can be used with other transmitters as well. There are three possible combinations with different advantages.

Use the external transmitter through iVol only.

Use the external transmitter as a student radio. The trainer can hand-over the signal in flight using one of the switches. This is the standard trainer/student function as practiced on the flying field. 

Use only some functions on the external transmitter and the rest on iVol. This way, the student can concentrate on some functions only without getting confused by the full complexity of flying. This is a very advanced version of the strainer/studen procedure limiting to dedicated functions only.