1st Video - That 120 fps mode does look good but the resolution spec for 120 is 640X480. I don't use 120 often and don't know the details but I'm sure the FH100 cannot do HD at 120 fps. The FH100 also has a special recording mode to produce files for the Youtube format. I have not used it. It looks from the signs as if the video is a Casio promotion.
The 2nd video uses the '30 - 240 fps' mode. The camera takes video at 30 fps and when you trigger it a second time it changes mode to 240 fps, back and forth between 30 & 240 with sound recorded for 30. A very good mode if someone is taping a match and wants to do stroke analysis on some strokes.
[Note: Youtube uses compression and the quality of stop action frame-by-frame is considerably degraded. Viewing the Casio FH100 video file on the camera's LCD screen or on the computer, using Quicktime, frame-by-frame works smoothly forward & backward.
You're right about the two-camera approach having big advantages. I have an Aiptek 60p fps and can do a nice job on the overall match and the 60p is also very useful for looking at some stroke features. But the 240 fps with the Casio does a great job for stroke analysis.