I did not really look into it but like you (since you asked the question) I have my doubts about it.
Why would you trust anyone/thing that ask the password for something your are paying for?
A friend once told sent me a link to a software that tells you who blocked you from MSN...No need to say that I replied to my friend that this was not a too clever move to install this: same as this gadget, it was asking for you ID and password.
It's like giving your car keys to a stranger...Stay away from this and just monitor it yourself. The task manager (when started) can count how much bandwidth is being used. So just start it before going to internet and leave it running until you're done and check how much you used. Much safer.
Cheers!