Depends on the hobbyist needs and if they have a controller already. If they have a controller it is somewhat easy. If they don't then they have choices.
GHL - you should use their product.
Neptune - you should use their product.
Neither or no controller - make a list of what you want a controller to do and then see which is a better fit for you based on what they offer and at what price. Do you want wave makers, pumps, expansion, dosing, etc. Each offer something some of which both do and some of which one does and the other does not. Don't get caught up on the forums product bashing of either - start with "your" requirements and off you go.
Follow up with not owning either controller is a Mindstream. Although they are admittedly by their CEO running into manufacturing issues be it demand or other - not my say - it will test and report on more items than GHL or Apex but will not do controller functions such as on, off, flow, or controller stuff. I raise this because GHL and Apex will give you base data which MS will provide so it will be duplicate. Salinity for example, ph, for another. Temp, etc. If you already have this in a controller then you need to ask self what does the MS add that the others don't.
For me the decision was a no brainer. I have a Neptune Apex so it made sense to go that route financially. Also I'll admit I'm biased - I've been using Neptune products for a long time and have had good luck and great support. But again since I had a Apex controller it made sense so that is why. Also reagent based testing is fine. We have been doing tests this way in the hobby for ever. The fact it is automated now it is at least consistent vs our manual effort. Not only that prior to the Trident I wasn't testing at all. So the fact it is doing it for me, well, means it gets done...
Reagent, subscription, take your pick. Reagents you can buy at 2 or 6 month supplies. I buy at 6 month and it is the better deal. MS uses a subscription base of 10 bucks a month. Maybe more, or less. I don't know - I just know it is monthly. GHL I do not know - I think they use probes so not a issue.
Personally speaking if I didn't own a Apex I would have went with GHL. Mindstream is a non starter for me nor do I believe it will be in the hobby for much longer. I could be wrong and hope that isn't the case for those who purchased it.
Best of luck to you.
