I saw a commercial for a product called Flex Seal and I was wondering if anyone had experience with it and could advise if it would work for a ventilation pipe boot on a roof. I need to replace a few boots on a very tall and steep roof. Would something like this be as good as putting a new boot on as far as how long it would stay sealed up and last? The site says it lasts for several years and doesn't dry or crack.

Site: https://www.getflexseal.com/

This is what they say about the material, I don't know how well mastic rubberized coatings work.
Q: What is Flex Seal™ made of?
A: Flex Seal™ is a thick, durable, mastic rubberize coating that is specially formulated to spray out as a liquid, seep into cracks and holes and dry to a watertight, flexible, rubberized coating.
I don't want to go through the trouble of getting on the roof and spraying it if it won't hold up over time. Would I be better off just replacing the boot or will something like this work?