No problem
I have no problem with the FBI or any other agency buying exploits, as long as agents do it with their own personal funds and don't get reimbursed.
Maybe the reason they keep missing opportunities to stop the enemy is that their real investigatory skills have been allowed to atrophy, what with their leadership becoming so enamored of high tech tools that (falsely) promise "more for less". All of this is more about middle managers and government "executives" seeking to be heroes at budget time than a serious effort to get the job done.