Testing static screens vs. interactive prototype – Which is the most effective method via UserTesting.com?

I am in the process of revamping a form page which the users were finding it difficult to attempt. Consequently, I have developed a prototype with some click-through interactions which is consist of about 3 screens - a form page followed by the pages for review and confirmation. The main objective is to test it with the users and see whether they will be able to answer all the questions in the form easily and move forward towards the confirmation page or not.

I have once used usertesting.com in past and what I have learnt there was when we have a set of screens (mockups) to test, we should include a description along with instructions to narrate every screen/step in the flow. However, in case of using an interactive-prototype we may not be able to guide them (or interrupt them) at the screen-level but to have only some introduction-text in the beginning. Considering these conditions, will it be effective to launch the test with a set of static-screens? Or the interactive-prototype? – Please suggest.