Both the Reality Note (SR V4) Manifestor and the DM: Reality Shifter deal with manifestation, but they approach the process differently. The Reality Note works by reshaping your subconscious mind and the world around you. You write down what you want in your notebook, and the field programs your mind and body to make those changes. It’s like setting an intention and letting your subconscious work towards it.
On the other hand, the Reality Shifter shifts you in another reality where your desire already exist and it’s available for you;
As for when to use one over the other, it might come down to personal preference and belief.
If you have a certain path you need to follow and tasks given to you from higher and Superior dimensions, and you use this field - it’s possible that nothing might change.
However, if during this time period you don’t have any “mandatory tasks” set, you might get the job regardless of whether it’s good for you or not. I recommend you get the field called ‘The Finder’, which will always find the best opportunities for you in all situations and areas of your life.