The phrase "sees how it flies" is used to describe someone who is experimenting or testing something out to see how it performs or is received. There are several synonyms that can be used interchangeably with this phrase, such as "tests the waters", "tries it out", "checks the temperature", "experiments", "samples", "tastes", "tries on for size", "puts to the test", "pilots", "assesses", and "gives it a go". Each of these synonyms can convey a slightly different nuance or connotation, but they all share the basic idea of someone trying something out in a methodical or exploratory way.