TTRS has advantages in that it does work on spelling/phonics, and it also uses a variety of skills like listening to the words and translating that into finger movements, copying words where you can see the fingers on screen, copying words where you can't see the fingers, and so on. It is the listening bit that I think makes it different from many others, and perhaps more useful in terms of what children (particularly those who struggle with spelling) actually have to do. It is also broken up into many many levels, with lots of charts and achievements, and lots of repetition - the words are learned via spelling patterns, rather than just teaching where the letters are.
Its downsides are that it takes a very long time, because of the many levels and lots of repetition! Some children get bored and don't complete the program. It's not 'fun' like dance mat or some of the other games that teach keyboarding skills alone. It's expensive.
It is the sort of program that takes a dedicated 5-10 min a day over a couple of years. I've not used it myself but know pupils who have and I've seen them using it.
It's the sort of thing that could be started in Yr4 or 5, to give lots of time to get through it at a slow pace. For a child in Year 7 who needs to get on with touch typing to use computers to do homework, then a faster keyboarding course would probably be more helpful. On the other hand, the biggest factor of all is motivation. If children want to learn, and are disciplined about using the correct fingers every time they sit down to type, then it doesn't have to take long to learn, whatever program you use.