This episode was tricky because of the number of voices I had to do. In doing so many it's easy to forget exactly how I did the voice. Fortunately, I've added voices gradually over time so I'm usually only dealing with one new voice. But I commonly find myself using the wrong voice.
There's a clear separation of voices in this episode which isn't always as apparent. I also did a slight separation for Walt's encounter with the little man and Charlie's encounter with the clown but those don't come across as clearly. The trick helps to distinguish each character as a separate speaker which can compensate for any slip-ups I might make. I also found the echo effect helped a little.
It's like a form of audio 3D. The brain initially hears a voice coming from a different direction and assumes it to be someone else. However, it tends to get weaker with long speaking parts because the brain adjusts within a few seconds. After that point it's only the difference in sound that works. So it works better when the characters are talking in short breaks. A good example of where it doesn't work as well is during the 25th day of the Christmas specials when the Blue Hot Gossip characters are reading a poem. But since I recorded it and I'm familiar with the sound of my voice it's harder for me to be fooled so I don't know how well it plays to other listeners.
There's something similar that happens with the Muppets. If you look at The Muppet Show you'll find times when Kermit, who was voiced by Jim Henson, is speaking with Ralph who is also voiced by Jim Henson yet they're taken as two different characters because we see two characters on screen. Although years of experience also helped him to keep the voices separate when speaking.