not useless at all, when used in the correct application they are very good but a massive overkill on something like an rs turbo.

external gates can be a great aid in boost control in instances like the T4 when even with the internal gate wide open they still make 15-20psi of boost as the internal gates are too small and not efficient enough to pass enough exhaust gas. an external gate of the correct size would cure this.

Also as external gates are often far better sized than internal systems,because they are not bound to casting sizes, they are more efficient in terms of flow, they will also make more power, because when the waste gate opens the engine in effect becomes a nasp, so a larger more efficient gate will increase ve when its open.