Billboard points out the great use  of playback during the performance of Britney:

“In particular,” Me Against the Music ” was one of the few songs during the show, where you could see the live voice of Britney. The vast majority of the show was in playback, and only occasionally a few sentences was apparently live. There was a certain thrill to hear Britney really breathe into the microphone – but it was very rare “

USA Today appreciates the show despite Britney little communication with the audience (especially in the preview):

“One wanted a little ‘more intimate by Britney, especially on the night of the preview with stars and celebrities on hand. But the singer with her shy nature that we have known in recent years ”

In addition, a defense for the use of recorded voice:

“With regard to the spectrum often raised the playback to begin with, these songs require different effects and certainly his voice had to be processed through the computer to get the tone that corresponded to what was recorded in the studio”