It is pseudo-free as I mention. You don't have to pay as long as you don't want to follow a word more than about 4 drills down. However even if you do, you can get to the 4th stage down and then take the word you're working on and plug it back in again.
I'm also not sure what you mean by "better implemented"?
Plus I wasn't necessarily suggesting you use it for this, but I have found it a useful site in the past and couldn't resist mentioning it.