Boost kick also has RCO lag. This phenomenon, if I remember correctly, is one where you retain landing lag even if you are hit out of the move. I believe the RCO lag is worse when you are hit out of later parts of the move, but I haven't tested it so I cannot say with certainty.
Either way, just consider that in addition to the "lots of lag" comment above. It's got immense risk to it, but immense reward if used at the end of a combo. It can also be used out of shield, but you need to react to a hit... don't just use it because you can. I've thrown away a few tournament sets because I've boost kicked onto a shield.
