Hi davidj, welcome to the A2oc and thanks for the tip on bargain priced oils from Costco.
The Mobil1 0w40 synthetic is a quality oil which meets VW 502.00 and VW 505.00 specs and is fine for petrol engines. If you have a TDi, the engine really needs VW 505.01 or 507.00 spec oil. Same applies to the Polo if it has the 3 cyl PD engine.
Cheers Spike