I'm not comfortable trading him. Mostly because I don't think Brisset is an NFL QB ( In case TB was injured).
Brisset is NOT READY to step in if needed in 2017, and maybe 2018, as the Pats seek their 6th Lombardi. From a talent standpoint he has a strong but not very accurate arm. His release is ponderous, and long, and I don't think his pass is very catchable when not accurate. Still I think he will be an above average BACKUP QB, eventually.
Garoppolo on the other hand, has that certain intangible but real, leadership talent, follow me attitude, that player's want to play for. It is a real talent that the military explicitly looks for in its officers.
He has a lightening fast release, approaching Marino. His accuracy is well above average, but not equal to Brady's short to intermediate accuracy; but then no one else does either. Still it is franchise quality accuracy.
Reality, is that there are not a lot of, and enough of, franchise QBs to go around. They are valuable enough to have high value, no matter the contract that he is signed to by his team. The Pats have him for two more years, including a franchise year, and the CAP room to keep him. You keep franchise QBs when you have them. Besides what glaring hole to the Pats absolutely have to fill, except backup QB if they were to trade him? Answer ZERO!
BB wants to have a deep team while seeking their 6th Lombardi. Brady and Polo do provide that, at that most critical position to have depth during the next two years.