Purchased Stan's sealant when I started riding my road bike with tubeless tires. The sealant works. I haven't had to repair a flat tire in 4 years. I also use Stan's sealant in my cyclocross tires. How do I know it works? Occasionally I will have a puncture and I will hear air leaking and notices a small amount of sealant exiting the puncture hole. After a few revolutions the puncture is sealed, and I keep on riding. I regularly pull goat head thorns out of my cyclocross tires and watch the sealant fill the holes while a small amount of air escapes. The sealant does evaporate so you need to add more sealant, frequency depends on temp and humidity. One thing to be aware of, most of the sealant is liquid with lots of particulate suspended in the liquid. I think the particulate is what actually fills the puncture holes. When you get to the bottom of a bottle of sealant there is usually not much particulate left. At that point your better off not using the remaining sealant. Best to start a new bottle with more particulate. Check out Stan's No Tubes web site on for useful tips on going tubeless and using the sealant.
I was skeptical about going tubeless for a long time. I avoided it until I bought a mountain bike and could really see the benefit of running at lower pressures.
With this stuff on board I don't worry about flats and I get to enjoy super grippy tires. It's so easy to use, it cleans up easy, and the punctures I've actually seen have all sealed up quick.
Well worth the purchase, my shop will never be without a bottle again!
It's good to keep this stuff around in quantity for my MTB and cross bikes. Swapping tubeless tires or fixing flats is less tedious when all the tools are readily available...Yeah and the bulk price is way better than the little single serving bottles.
I have used Slime and Air Lock over the years and I have been thoroughly impressed with Stans. Really nice to use less sealant per tube and my instinct is that Stans seals punctures more quickly than the competitors, reason being that I have had to top up my tires less frequently using Stans than either Slime or Air Lock...I assume I have experienced a roughly equal number of puncture events using each of the sealants. I was initially put off by the limited servicelife of Stan's-sounds like it's supposed to dry out after a year or something-but if you live in a high puncture environment (as I do...Alb, NM) then chances are it won't be able to dry out before you need more any way.