Have you played with this number at all? 10 phrases per day seems awfully low in my mind. If I was to download this extension, I would want to use it for a day or two before paying for an upgrade. I imagine you hit 10 phrases quite quickly, and this might turn some people off of the product before they fall in love.
You could be right. It used to be 20 for free, but I lowered it so that more people would actually hit the limit and get the "Go Premium" message. It's hard to know what the optimal number should be. For a while I had a split test running where some users had 5, some 10, and some 20 per day. But there weren't enough users to see a significant difference in conversions.
