What we always do when practicing footwork is starting at a slow pace (just walking), but making sure you take the steps in the right way, also remembering how many steps you need and taking in notice how far on the court you have to go to reach a shuttle.
After that do it little faster, then top speed, little faster and slow again.
Our trainer always watches if we start making mistakes after doing is really fast and if we still remember how to do it correctly (when really tired) when we are doing it slow the last time.
The Rasmussen video is a great example of a practice that's good for learning and maintaining footwork quality, and if you had to pick just one style of practice, maybe this would be it.
However, it's also useful to practise footwork at full speed sometimes. It's often difficult to transfer technical skills learned from practice into games. Using increasingly realistic (i.e. game-like) practices is important for improving this skill transfer.
In particular, agility cannot be learned without practising in response to a stimulus. A lot of footwork training forgets about this. This is where a partner comes in handy, or possibly a recorded audio cue.
That doesn't mean the "basic" practices become redundant. That Rasmussen drill could be useful for any level of player.
A very good point about being realistic to a game situation and one I keep raising with our coach. We are constantly tweaking his routines with input about being realistic about the movements, which helps us and him.
Our coach occasionally number the corners (randomly) and instead of having someone pointing, they say a number. Suddenly makes it a lot more realistic.
With regards to the footwork exercises, we take some footwork drills and make them 30 seconds controlled then 15 seconds fast with no breaks inbetween. I think it's pretty good.