I've had excellent results with RainX, except for the slightly noticeable haze I cannot get off when I initially apply it. To get it off, I wait to the next day and use some water and a rag to remove it.
Anyway, I've only used RainX, haven't tried the Castrol brand yet. But I can tell you, I live in Louisiana, where rain is no stranger, and on my Explorer that is 2.5 years old, I can say that I have never used my windshield wipers. Water, no matter how heavy rolls right off.
On my car, I've used Zaino Z2 on them, it works ok, but I do not think the beading is as pronounced as with RainX.
If Castrol produces similar results and wipes off clean, I will definitely give it a try.
Brian