Tried it in my garage a week ago, very tiring. Good luck with it
Think the emphasis on this exercise is speed and lunge form.
Make sure that you dont go over 90 degrees on the lunge, in other words do not allow your knee to go past your ankle. If you do, it means all the recovery power is lost in the lunge and you have to pull yourself back to base with your glutes rather than push with the leading leg.
That's a bold claim I'd be suprised if tiredness wasn't an issue, it's an exercise designed to be sustained until exhaustion (you can see the kid slows down alot in the 50 seconds). Muscle fatigue will set in after a couple of minutes if you try to maintain the pace shown in the video.
It certainly will help your speed though, I did some normal shadows after a rest period and they felt easier. (I'm 6"2 so moving with this agility is considerably more difficult for me).
Edit: I moved the circle out to a slightly bigger radius too, because it may be that this isn't large enough for an adult player.
That is great to combine the two infact (when I said I combined it with footwork I meant that video)- it is probably worth noting that they're very different exercises with different intentions.
The 8 point exercise is high intensity and deep lunging with little recovery period. It will encourage pick up of difficult shots and decent recovery towards them with raw speed.
The rasmussen exercise is more stamina/ endurance based and is more focused on correct footwork. It will encourage consistency rather than raw speed. It has a longer time, he says that your recovery is slow.
Both are essential to your game, because sometimes you do not have the luxury of long recovery periods between shots.