I don't think you should use either the future in the past in this context in the English phrase or "было бы" in your Russian translation. Doubt and uncertainty can be expressed by the words "rather", "quite". On the other hand the word "impossible" doesn't express doubt, on contrary it denotes assurance, certainty.
On the other hand, if it's a kind of ad, I wouldn't recommend to use negation. It's better from the psycologic point of view to put everything in a positive way.
So, I would say:
Несмотря на то, что схема расчёта выплат по данному продукту довольно проста, довольно/достаточно трудно [для неспециалиста] воспринять все её мельчайшие детали/нюансы.