It hardly touches the issue of benefits. A four year graduated reduction of in work benefits over a one off seven year period (emergency brake) and then after this we can't apply these reductions again( I'm still not sure whether we have to get permission from the other member states for the emergency brake).
The impact on the numbers of migrant workers will be minimal and it will save about 2s/6d.
I'd imagine it will actually cost a fortune when the minimum wage rises to a living wage, assuming cost of living will rise and welfare payments will rise accordingly.