I am also a fellow maul player and I never change to secondary weapon at all in duels or TO. I use it the whole time, because it is a challenge for me. I love this weapon.
The best thing is the stab. I always trick people with a stab, which I know won´t reach the opponent. Immediately after the stab I use the overhead slash, because I know they mostly charge in.
When I started with the maul, I had great difficulties against shield users. But I managed to get around it somehow. Kick, sideswing and run past the enemy looking slightly back from your point of view. It will hit the back of the opponent. And after they are aware that I use kick, they tend to try to go into the offensive. One stab will be blocked, but I use another stab, which kills the enemy, because he thinks that I won´t attack a second time or maybe kick him :D .
You can play the maul defensively, but you have to watch very carefully. Make it look like you are retreating, look at the movement of the enemy (he will pretend to attack, but he won´t get past a certain distance). If he does, you launch an attack and runs towards him.
The only thing I must acknowledge is the thing that if you hit the opponent hard, he can instantly attack you again. I saw this happening against a knight. All other classes are affected by the hard hit, but the knight seems not be affected by the “stun” effect or whatever it is called.