I use Continental Revo Sealant in my Contiental Tubular tyres (Conti Competitions and Podium TTs). As a test, when I tore the tread off a podium TT (locked rear wheel) but it was still inflated I decided to try an experiment. So I got a 1" pin nail and hammered it into the inflated tyre. No loss. Pulled it out, some hissing. Rotated wheel once. It was sealed!!!
Tried again - SIX more times with six more pin nails. Sealed each time, once rotated. So I got serious. I hammered a 2" round nail into the tyre. Again no immediate air loss. Pulled it out and it hissed. Rotated wheel once and it sealed.
It seems to me that the fresh sealant moving around when the tyre is rotated does the job.
Personally I was impressed. It is in all my TT bike Tubular tyres.
However last week I had a sudden blow out from my front Tub (an almost new one) and the sealant did not work. Air would simply not stay in tyre even with track pump. Completely flat. I can only assume when I hit the hole it split the inner tube. Fortunately I was only 400yds from home. I hope this helps.