See what I'm talking about:

These people would get so much more out of their workout if they had a visual motivational stimulus. The tones in this room are so uninspiring. There usually is a mirror on the wall - doubling the drab shades and increasing self awareness. Whilst self awareness may be important for technique and safety, I believe the participants would get more out of the workout by taking their mind to a less self conscious state which would allow the body to move in ways that conscious restrictions don't allow due to social conditioning.
Another of my major concerns if the pressure on the instructor - here you can hear she is having to fight against the noise to get the instructions across as well as doing the workout and motivating the team. Visual instructions would inform the audience and free the instructor up to focus on additional motivation and technique improvements.

P.S. Notice the tall bloke, bless him, he is all over the place. He's stepping back with the wrong leg. This kind of mistake happens often. Even though he can see the instructor and everyone else in the room on the wall mirror, he keeps repeating the same mistake. Now, with a screen giving the instructions to the group, this would free up the instructor to address him and help him correct his movements to maximise his workout and not look such a fool.