As far as I am aware, there isn't a manufacturer, certainly in the UK but possibly the world, who gives a guarantee with their protector. I'll repeat
NO ONE What you will find though are lots who offer an insurance policy against accidents. There is a huge difference. It is impossible to make a carpet or fabric stain proof. The best you can do is make them more stain resistant. The insurance is for when "more stain resistant" isn't enough.
As for Flouroseal, I have found it to be a superb protector if correctly applied. I'll repeat an often told tale. I applied Flouroseal on a new plain pastel green wool axminster carpet. Cleaned annually 3 years running without top-up (exceeding normal recommendations) Customer has party. Lots and lots and lots of red wine etc. spilt on carpet. It looked like the day after the Battle of Bosworth. Red stains on green
All that was required was a rinse with Liquid Woolsafe. No pre-spray. No spotting. No Red RX. No worries.
Safe and happy protecting:)
Ken