I have always used a 10x loupe for competition cutting. It was good enough to be 3rd in the group of 5 cutters that finished 2nd in the 2014 Australian International Faceting Challenge. It is my understanding that the USFG competition is judged using 10X loupes. If I am wrong I am sure I will be corrected.
For fun cutting or commercial cutting making precise meets is overrated. I only check the first meet in a sequence and use my Facetron dial for the rest. With a hard stop machine one can just use their ear. With practice your meets will be good enough. No one other than yourself will notice or care how close the meets are if they are not visible to the naked eye. The material, color and shine are what is most important.
My advice for a new cutter is to not spend too much time on one stone trying to make it perfect. Get use to your machine and with time you meets will get better and better. I still keep the first stone I cut and it is still beautiful to me with all it’s near meets and scratches.