Looks like GHL will get my business instead
I thought about the costs versus goning completely with GHL too, as I am a GHL user. The KH director + plus required dosing pumps is $859, and that measures just KH. GHL is developing the ION director, which will measure Calcium and Mag and that will also need 2-3 pumps. I imagine that the cost of this will be about $859 as well. So, we are looking at about $1700 to measure 3 parameters. That's not cheap, and is about the cost of the Mindstream for purchase and 2 years of use. With GHL, you would have to purchase a controller to also monitor salinity and pH, etc... like the Mindstream, which is another $500+
To be fair, the reagent costs and the maintenance costs to keep the GHL units running and calibrated will very likely be less than $35 per month, so going with them could be cheaper in the long run. (Not to be discounted is the likely greater user labor to maintain the GHL units and set them up, whatever that is worth to each of us.) And, GHL allows you to CONTROL those parameters as well and this is very important to many users. GHL also has a good reputation for quality and is not going out of business anytime soon. These are all good things to consider, but IMHO saving money over the first year or two of use is not likely to be an advantage to going with GHL.