I didn't really like the T-foil, you pretty much get what you paid for it. It feels and seems built like a play kite, not a power kite trainer.
It is good for kids; I'd started out with the the Best 3m trainer, but that was too much for the 6-7 year olds to handle.
For grownups I'd get a 3m or slightly bigger They're small enough to act as trainers if you don't go out in really high winds, and big enough to be fun in high winds - when it's blowing and you can't get to the water, just flying the big trainer is surprisingly fun, so it's not a wasted purchase after you've learned to kite.
has a good section reviewing the pros and cons of various trainer kites.