I finally caved in and purchased the Rivitalash during the Nordstrom anniversary sale; it was buy one, get one free. One tube lasts 6 months, so next July, it will be time to buy another set (so far, they've done this every year since they started to carry it).
I researched all the other ones out there including their generic versions you can purchase on other sites. A YouTuber that I respect (and is almost 60) achieved amazing results with it; she also uses the primer and mascara.
It is exactly 6 weeks to the DAY today that I started using it and the difference is WOW!! My lashes now hit my glasses with one coat of mascara. I also use the primer but only applied at the base and not pulled through. This way, the serum coats the top at night and the primer coats the underneath during the day.
It's an investment. If you stop using it, within a month you will lose ALL the benefits you gained.