I can't understand how guys say this. TRT is usually 100mg per week, which translates to ~65mg of actual test (depending on E or C ester). This is enough to put most guys into the higher natural ranges.
300mg is way more than anyone naturally produces, and I know from personal experience that you will still see decent gains from it (if it is a first cycle).
But yeah, I wouldn't worry about the little bit of water retention from it.