You can use 2go.aero for free and still have a good product with 90% of the questions you have with Aviator.
With Aviator you can use it in the "study" or "examination" mode. The former you can load all questions by default or in a test mode: random order or limited time. What is also great is that you can choose to load defined chapters. For instance, if you're doing Instrumentation, you can decide to load questions related only to pression instruments.
If you choose examination mode you can simulate the examination being limited in time and have random questions.
As I told you I think it's a little overpriced as you can get most of the questions for free online, but the product has some extra features which makes it still worth.
