Sounds interesting... maybe it is something different this time. I looked over the user guide, and it is NOT an ISE-based monitor. It is a KCl junction type electrode, so it may be more resistant to Mg and other Ca-similar ion issue.
Similar to pH monitor, the probe does not last very long. The user guide say replace it every 18-24 months, and I bet that would be between $50 to $100. Furthermore, there is a fill hole that user need to add KCl solution into, and so if they can come up with a sealed electrode version, that would make it easier for general public to use.
If you do monitor calcium regularly, the initial cost and probe replacement can be a small issue, but for people who only do calcium monitoring seldomly, it may not be that good of a deal. If you do aquarium maintenance, that would work out well too.
For local reef club, it can be a good idea if the club get the monitor, and each of the member get a private probe. that way, they can share the resource, and make it more affordable.
A: The calcium monitor is missing in the Club's cabinet... who used it last time?
B: Jason did, he toke it in the Club meeting two months ago...
Jason: I return it last month already....
Anyway, let see how accurate it is when the report come out...