Michael,
LoadNinja and TestComplete are different in their intended purposes.
LoadNinja is SmartBear's load delivery application. It is hosted by SmartBear in Amazon web-services and is designed for ease-of-use in developing scripts using the bulit in recording tool, to provide load to web applications and APIs for the purpose of evaluting those systems under loaded conditions.
TestComplete is SmartBear's premiere UI functional testing tool. It also has a built-in recorder for easily creating tests to evaluate the functional perspective of a given web application or desktop application. It is much more robust than LoadNinja in this regard.
Ideally, you can use TestComplete to create tests to functionally test your sites and web applications, then use LoadNinja to build load tests to see how those sites stand up under load.
For more detailed information, please visit our site, or reach out through the online form for a representative to contact you.
LoadNinja: https://loadninja.com/features/
TestComplete: https://smartbear.com/product/testcomplete/features/
Cheers,
Mel