Having undercoated hundreds of cars over the years, my first comment is that anything is better than nothing. Living up in the Ontario rust belt, I have seen first hand the benefits of oil based undercoating. Having owned a body shop, I was always busy in the fall undercoating vehicles. I have tried everything from used oil, to my own mix of new oil-tranny fluids-wd40. I finally settled on “fluid film” as my go to undercoating. Bear in mind that although anything is better than nothing, a product is only as good as the person applying it. Up in these parts it is an applied annually. Cheapest bodywork you will ever do.