I tested a lot of contact form plugins, this is definitely one of my favorite plugins.
It delivers a great functionality for free and if you have special needs you can choose one of the premium extension (e.g. Paypal). If you need a couple of them it would be nice to have a developer edition.
Will keep on working with the ninja.
Bring up a little bit more functionality to modify the styling.
e.g I want to decide where to put the * for required fields or the information where the hint is displayed.