Originally Posted by Gakure
He's a coward though. Has haki but still goes around with seastone embedded in his weapon
I wouldn't call him a coward for using every possible advantage in a fight.
Besides sea stone is better than haki in a few ways. It subdues the DF ability and weakens the DF user. Haki just protects from/negates the DF ability on the haki user.
There is no reason to throw away an excellent weapon just because you have a new one.