The VoiceMaster Pro insert send is unbalanced but the insert return is balanced. The reason for designing the unit this way is for practicality.
The insert return is electronically balanced and will accept either balanced or unbalanced signals. The send is unbalanced because it allows you to connect to balanced or unbalanced inputs on another device without problems (thus giving the flexibility of being able to connect to a wider range of devices e.g guitar pedals etc.).
Connecting balanced outputs to unbalanced inputs can result in signal attenuation whereas connecting unbalanced to balanced is less problematic and can be done using a standard unbalanced 1/4" jack cable.