The upgrade policy of ReefMaster is that all minor version updates are free, but that upgrade charges will apply when moving between major versions.
For example, we are currently shipping v1.5 - all updates since the first v1.0 release have been free for all users, and will remain so until we reach v2.0. When we do release a version 2.0, there will be a charge to move from v1.x. The upgrade cost will be at a significant discount to the cost of the whole package.
This upgrade policy is a common one for software, and of course there is no requirement to upgrade - you can continue using v1.x for as long as you like. The rough game-plan now is to have a v2 sometime around the middle/end of 2014 - so something like an 18/24 month cycle for major versions.
We will also be releasing some paid additional modules, such as bottom hardness and sidescan mosaicing, within that time-frame.
Matt