V mount and Z mount
The V and Z platforms both solve the problem of having your ballhead at an awkward angle when on a star tracker. So what's the difference?
The V platform is for those who want to save weight. If you're already using a heavy setup you may not have much room to add weight on top of the MSM which has a payload of 3kg.
The Z platform has the added benefit of being able to be used to replace the ball head on a tripod when not using a star tracker at all. You can also use the Z platform as a table-top tripod. So it's an exchange of versatility for a little added weight.