Previously, I have charged $4.99/year, $19.99/year, $1/month, $4.99/month, and $19.99/one-time is the latest price. You're right that the sample is too small to make much of... on the other hand, it is double what the tool usually makes per month.

I'm happy to experiment, my main question is: am I missing out on the bigger picture by charging for this app instead of using it to promote TweetingMachine? I'm not convinced that the target audiences are the same... but guess I'm going to have to do another experiment ;)