Unfortunately, the answer to this question keeps changing! For almost a decade, golf rangefinders have been allowed for normal play if permitted by local rule. In 2016, the USGA extended this to include amateur competitions. The next step was to include PGA practice rounds but not tournament play proper. Recently, rangefinders have been allowed on a trial basis in several PGA-backed tours, but only for calculating distance, not wind, slope, or elevation. For the moment, you'll need to check rules on a case-by-case basis.