I've read you can get something from him later on. Is it better to wait?

From this walkthrough:

[i]Talk to Tek'elach and find out that he has a hidden agenda by helping you.
After a few future events occur, it's clear what he's planning and why; but
it'll be a mystery for a little while longer. Kill him just because he looks
ugly, or you may want to wait because he will show up again later if you leave
him alone.[/i]

No, don't kill it, talk to it, you get great info about some parts of the story, you will understand once you learn that part.