I've heard that they are more reliable. I have heard that the walbros fail sometimes and the mkiv pumps do too. But I have NEVER heard anything negative about the 300ZX TT pumps. I am going for optimum reliability.
I will be trying the twin in tank walbros in my car soon, the twin MK4 pumps are very big and I dont think they will fit through the hole in the tank. The 300zx pumps are the same size as the mk4 pumps. They very well might be the same pump built by Denso.