I ran out of petrol today on the motorway and was walking along with my petrol can and someone stopped to give me a lift

There wasn't a shell garage about and the nearest one only sold normal unleaded. I've never used it before but didn't have much choice so filled up my can and bought a wee bottle of lead additive just to be sure.

Put the petrol and additive in and after a few turns away it went

So, is this just as good as optimax etc or would it start running crap after a while?