Don't get me wrong: it is strong, robust, powerful and feature-rich... but it's not intuitive. I hope the developers will look into that in the future.
If you want to use this extension--by all means accept my recommendation--and be sure to put on a pot of coffee as you set it up.
It gets a little frustrating at times when configuring authorize.net, but its is still worth the effort.
I'd like to see a lot more in the way of reporting and tools that are of more use to a larger ecommerce site. Processing orders is still a little cumbersome from the back end.