Luddites crack me up. Seriously, this could be said about every single technical advance in history, from the toilet to the internal combustion engine to the internet.
The internet has sites I don't care about, some of it is inaccurate, hence causing concerns, is more expensive than not having internet, and definitely not necessary. Heck, current testing kits have accuracy concerns! And sometimes, it really is just about convenience. A hole in the ground in an outhouse is cheaper than a toilet, but I'll take indoor plumbing any day of the week.
I'm a data guy. My bike computer can track my HR, power output, speed, altitude, and pedal RPMs and then parse it in myriad ways. Is all that necessary to ride a bike? Of course not, but it's fun for those of us who like to discover the correlations between effort and results, and find more efficient ways to make gains.
Same thing here. It's not about chasing numbers, but about getting a better understanding of how parameters are interrelated with themselves, and how various changes affect them. It would provide a much deeper understanding of our water chemistry and its effect on our livestock.
Is it necessary? Some people argue protein skimmers aren't necessary. Some argue that regular testing of water parameters isn't necessary. But for those of us who want a deeper understanding of what is going on in our tanks, this would be a godsend.
The price of the disks has to come down, or their duration has move beyond one month. Those are real concerns, but I really do love the whole "bah hambug technology!" thing that so many have. No one is forcing you to buy it or connect anything to the internet or surrender your horse and buggy. The Amish lead rich, rewarding lives despite their rejection of modernity. Your fish and coral will do fine without this gadget.
But if people want more information, that is also not a bad thing.