I'm not sure it's only a "bonus". Russia will weather this thing just fine although not without some of those budget adjustments the article referred to. Iran may not.
With just a sliver of oil sales income remaining, domestic unrest, inflation and disease are turning the Islamic Republic into a failing state.
The strategic benefit to Saudi Arabia of having Iran hamstrung over this is considerable. Iran has shown the world how easy it is to obstruct oil through the Straits of Hormuz with thinly-veiled special operations tanker terror attacks and how easy it is to attack major shipment facilities with drones. Saudi Arabia does not have the naval resources to perform the escort services itself and greater oil independence promises to reduce the willingness of its customers to perform that function. This moves the arena from the military to the economic, where Iran is far more vulnerable.
It could, as a "bonus", make things difficult for U.S. shale/fracking operations if the Saudis could hold prices at this low for enough time, but that may turn out to be more expensive than it's worth. We'll see.
I find little admirable with Saudi Arabia but the old saying is that the enemy of my enemy is my friend. If they break Russia and Iran economically with $25 a barrel oil then so be it. I would rather have the US fracking industry suffer a short term economic hardship than loose any more US soldiers in Iraq or Syria. We broke the Soviet Union this way without resorting to nuclear war. I think Trump’s strategy is bearing fruit and American soldiers are not dying.