Fuzion is great; easy application, solid durability, and a very sharp look.
If you look at the page for the regular Fuzion which goes for $175, you will see multiple reviews. The 3oz sample size came out much later after the regular 16oz Fuzion so there are no reviews as of yet.
Clean your paint with Wolfgang Paintwork Polish Enhancer or do a simple alcohol wipe-down and then apply the Fuzion. The Pinnacle Cleansing Lotion will work nicely, too. If the paint is in decent shape, it will make the car look great. If the car is badly swirled/scratched up then it will only highlight the imperfections.
I wouldn't layer Souveran and Fuzion. Fuzion darkens the paint just a bit, while giving awesome depth and reflections. Very very intense reflections. I don't think that Fuzion and Souveran are meant to compete with each other. Souveran is more traditional with lots of depth and warmth, while Fuzion is about the reflections.