With zero prep you are just promoting any rust to carry on developing, as mentioned above it doesn't contain anything to cure rust or stop itI can’t recommend it enough!
The zero prep needed is worth it alone, takes hours of graft away from the task.
I happily re apply year after year as it really isn’t difficult at all. It works very well indeed.
Regarding the smell, I actually like it! But only because I like farm smells for nostalgic reasons.
One thing I didn’t expect though was for my dog to be so fascinated with the smell… she can be regularly found under my bus, sniffing the belly pans for the first few weeks after a Lanogaurd application.
I say go for it! But be prepared to check under your bus for animals before driving off each day.