It is a wonderful tool, but i often get the best results if i have a decent mix.
1take care of the low end, get busy with the high pass filter on the tracks
take care of your drum peaks. Apply compression, limiting, clipping on bass drum and snare. Then again on the drum bus. Saturation too.
Then let the mastering assistant do the rest, play with the final eq a bit in the mastering assistant.
Always A/B with a good commercial mix. Just use quicktime or Apple music to make things simple.
-14 LUFS is good enough. (That is where the assistant sets the mix. )
If you want much louder, your results may vary.
When analyzing the assistant says 'building a mastering chain'
Pretty sure there is compression and multiband compression going on in there. You get pumpung if you have too much peaking in your mix.