Doesn't using Netlimiter rely on trust, as each person could simply disable it. So why don't you both set download speed limits in your downloading programs, and if they can't I'm pretty sure you could find alternatives that do.
That would probably improve general usage like browsing etc especially when the other person isn't downloading something, then browsing could eat into that spare bandwidth.
I think it is just easier using net limiter than trying to govern individual applications like your web browser, download manager & torrent client etc.
been reading through this post for future reference as I am going to be faced with the same problem in the future, regarding the trust issue, assuming net limiter has some sort of password protect, you simply choose the password for the other machine and vice versa, problem solved
Essentially it is based on trust. You can remotely control other netlimiter pcs as a admin.
But, this is really not secure. Simply stopping the service or application would be a easy work around.