Waste of money IMO, it's just a rebuilt BC gearbox with IB5 bearings and a RST LSD fitted.
Go get an IB5 from a MK5 escort for £25 and wack your diff in, the IB5 also has more webbing on the casing to help prevent flex so is a little stronger too... Yes it bolts straight up

Oh whatever you do they will both drive just the same as a normal RST box, as essentially thats what they are.