I think, in general, you should be wary of anyone claiming anything is:" even though officially it has the highest success rate of any medical treatment on the NHS." That is not the language used by reputable researchers.
NHS treatments include: having your appendix out, measles vaccines, dental work, painkillers... all of these have objective outcome measures for success and are extremely successful treatments.
Any unnecessary or cosmetic treatment claiming to be more successful than the lifesaving act of whipping out an appendix when all you can measure is regret/happiness immediately after surgery despite worse physical health, is the language of a snake oil salesman.
I actually think it's closer to the true meaning of transphobic to give trans people a lower standard of care, with very little honesty or informed consent, as these claims do.