You could actually use this to rotate pretty well any content. It doesn't include a form for people to create testimonials - you have to collect their comments and create the testimonial posts manually.
Yes, it's simple, but what do people expect for free? The developer could create a more complicated plugin (a 'pro' version) but he'd be sensible to charge for that. The key to the strength of this plugin is in the description: "It's designed with minimal CSS so it will blend with your theme and can easily be updated to match your theme by your developer." You will only see that as a weakness if you want something all-singing and all-dancing out of the box.