Not sure id add a second brand of sealer. You could cause serious issues that you cant fix easily if their is any kind of problem with mixing them. I had a customer put ceramic block sealer in his engine oil instead of the coolant and instantly seized the motor. Obviously your not going to do that but mixing could cause issues if it hardens wherever it feels like.
Also every brand of sealer that says it fixes head gaskets,cracked heads,etc always shows it working and ive never seen one actually work in the real world.