Cracked Engine Block Sealer

I’m looking for comments on several of the engine block sealer products - K&W Nanotechnology, Blue Devil and Moroso Cermaic Seal. If you haven’t used one or more of these products please do not respond. If you have used any of them let me know what kind of results you had and also let me know if you followed the instructions to a “T” or not. Thanks

I used K & W seal back in 1961 on my 1947 Pontiac 6. This was a flathead engine with the valves in the block. I was getting coolant in the oil, so I pulled the cylinder head and found the crack in the block around one of the valves. I put the head back on with a new gasket, and used the K & W seal as directed. It worked as long as I owned the car and I saw the car on the street 2 years after I got rid of it. I assume that the K & W seal held.