Will this not result in the third dropdown being populated without selecting anything in the second dropdown? If so then i think it is also not correct.
I have seen multiple dropdowns where the second and third jump back to their default "choose" value when the first dropdown is changed but i have to state they used AJAX technology to update all dropdowns. So i wonder if it is possible to create the same effect with Dynamic Dropdowns.
I will give your suggestion a try later to see what happens.