Tried to use this recently. I don’t understand the decision to limit the free version to versions < 3.6. It would be beneficial for you and your users if you at least have a free trial for versions above 3.6.
I was suggesting that, for you to make more $$$ from it, its better to provide a free trial period for the said version.
It's documented very well, extremely easy to use and the pro version is priced very well.