Agree. I don't actually consider it a fail. I generally treat forays like this as exploratory research, and like many other situations, you have to pay for information.

6 invitations != 6 conversions, but yes, I'd agree that 25/conversion would be pretty reasonable. I haven't done recent metrics on what my customer LTV is, but its at least in the ballpark of 25.

I entirely agree that this needs some split testing -- I didn't explore the reddit advertising tools enough to see if there's an easy way to split test, but it didn't jump out at me.