I like
Thrasymachus (I also use
Athenaze,
Reading Greek, plus White's
First Greek Book, supplemented by bilingual versions of Xenophon's
Anabasis, and the
New Testament for reading practice.) I haven't gotten very far in Thrasymachus, though. I kinda got side-tracked by the other books.
I especially appreciate the book's brevity and the 2-3 pages of selections of authentic Greek at the end of the lessons. The story is a bit juvenile, but it's at least different from the stories in
Athenaze and
Reading Greek. The grammar and vocabulary support are minimal, but there (the website, "Learning Greek with Thrasymachus", at
http://www.vroma.org/~abarker/thrascontents.html has an accessible introduction to the grammar). The book places the burden on the teacher (or the exceptionally motivated and resourceful student), but it's helpful that the paradigms are included right after the units where they're introduced.
Are you thinking of using
Thrasymachus to teach, or to study? (I have an ulterior motive in asking that question--I lost my study partner for
Athenaze and would benefit from discussing that or any other book, lesson by lesson!

)
Lee