Both products work well in converting surfaces into a usable chalkboard. Except for the difference in drying time between these two paints, which Krylon is more prevalent with only 24 hours of curing compared to 3 days with Rustoleum, it seems that Chalkboard brush-on of Rust-Oleum is the winner.
Besides, once cured, the board can be erased easily and is much more durable than Krylon, even when being cleaned with soap and water.