This stuff retails for about $30 - $35 for 300ml locally so $44.60 for a litre if you already have Prime seems like a bargain. Use to restore waterproofing in wet weather gear after washing with Nikwax Tech Wash (or any other type of pure liquid soap). Good stuff.
Video about why you need to restore waterproofing from time to time here: https://m.youtube.com/watch?v=yAmXi8-Zcv8
Can this stuff make regular denim jeans waterproof?