I did my grill, bumper, wheels in the flat.
Looks good on bumper and grill but didn't care for it too much on wheels. It held up well but its too rough/flat for my tastes. Left it on for 6 months then bought new wheels/tires.
I then redid the grill with the glossifier. I really like that. Just did one coat of it at the end, gives it a good little shine. Its not the same as the plastidip so be prepared when you spray and use a good ventilated location. It also takes longer to dry so you can't wait 4 hours and just mount stuff. Over all though its great stuff and cheap.
The best thing I did was the interior pieces in white. I like the way it stands out and it give some character. These where in just flat white but its held up so well I didn't redo it with glossifier.