Nice looking pen!
As for ebony cracking, so far I havnt had any crack, then again only have made two pens with it. But more to come..
In talking with a good friend of mine, who builds custom pool cues for a living. He advised to make sure when glueing in the tube to coat the entire tube with ca, making sure to not have any sections without a coating of glue. Also once the pen is turned to size, a thin coat of ca on the out side and the edges to seal. Let fully cure then lightly sand and finish as normal.
He uses ebony for butt sleeves on the cues and they are often not much thicker then a pen..
Dont know if it works yet, but worth a shot..
Dennis