I've been using this on my Thunderbird Forum for six months. Works great. Also, like that users can use paypal or credit card. I renamed the phrase pay with Authorize.net to pay with Credit Card because most users don't know what they means. Also, this doesn't have a confirmation page after they pay which could confuse users.
The add-on does what it says it will. Doesn't cancel, but thats an issue with the authorize.net gateway API. Hopefully that will be fixed by authorize.net soon and then we can have that. But the add-on itself does the best it can. Good work.