I agree, Suzi! GD often causes depression and depression usually has a good measure of "why try? I'll just fail anyway." The longer you wait for that commitment from a child the more likely that helplessness will set in.
Also "1 in 300" change their mind and "phases" last six months? For a reversible procedure the right protocol seems to me to prescribe blockers for one year while evaluating the child psychologically if they're in danger of beginning puberty. If they're "1 in 300" a years delay means nothing.