Sika foam vs concrete for vinyl fence installation

Anyone use this expanding foam stuff before? While making plans to replace my wooden fence with vinyl I stumbled upon this product as a replacement to concrete. It seems almost too good to be true. A one pound bag of this liquid foam replaces 100 pounds of concrete and the price is reasonable ($10 a bag). You dig the hole, hold the post level, then pour in the liquid. It expands in about two minutes, hardens about 3-5 minutes after that and completely cures in two hours.

I went this route a few days ago and was impressed by how easy everything went. The fencing went right up since the posts cured so quickly. However, there's a fear of uncertainty because the foam is so damn light. I feel like at the first 30-40 mph wind storm, my fence may topple over.

Has anyone used this before and if so, what was your experience?

On a side note, pulling 32" concrete footings out of the ground was absolute . I wouldn't wish that experience on my worst enemy, especially when they break apart underground.