It's not cheap for how little I would use it. In my opinion the app is just not worth $20. I understand that you and others might feel different.
And don't get me started on AT&T and the RAPE they are giving people to use THE DATA THEY ALREADY PAID FOR. It just makes me want to go out of my way to abuse my "unlimited" data (during off peak hours of course).
I feel like abusing the data network. I'm unlimited. And I wouldn't wait for off peak times.
Back to the OP's question: I was told about a Cydia app simply called "Tether". It's by BigBoss. I downloaded it, but I don't have anything to tether to yet. It had a trial period, & said the paid version is $5. My only other "issue" with the app is that is had a spot that says "bill date". It really didn't explain what that was, nor have I tried to email the developer. The person that mentioned it to me has not answered my questions about it either.