The new Astra OPC's are pretty troublesome, seen a lot of them with gearbox issues, and with GM pulling out of S.A, this could be a concern. But if you really want one, I'd trade the 118i.
The current gen Astra OPC has a lot of issues. If the car still has warranty, it should be fine, otherwise, I would stay away. Best to ask the guys on the opc facebook page for advice.