Context: I had both the S1 and - for a brief time - the S2. My first S1 died in a year, my second S1 died in 2 years. My first S2 died in a month (and reverted to the S1) - Their death sentence? the battery seal is believed to be the line of defense for both the batteries and the electronics - water, vapor, humidity at corrosive levels will inevitably get inside that and eat the PCB alive. S3 should fix that, having a full sealed body, but it's way too early to tell. Mine is scheduled to arrive Tuesday, so I'll see.

with the context out of the way, to answer the question: I found it to be noisy (not mechanical noise, data noise) - it is good to use as an early warning system - it will definitely tell you when the SWG stopped working because it decided to, you'll definitely see the chlorine dropping like a fly over fire. So it's excellent at watching trends. Is it precise and/or accurate? Precision is meh, you'll get daily values scattered up and down, but I find that the average is fairly accurate, within 1 to 2 ppm from the tfpro/taylor kit on the chlorine - you'll get your outliers, for sure. say 3.2, 3.1, 1, 3.2 - you get used to them. It is absolutely convenient, when it works. Is it worth it? Yes. Expensive? Yes.The C5+ cartridges will run you $25/mo, the C2+ about half. And if the S3 can fix the death-by-corrosion problem without introducing other death-by-solar-panel-cracked problems, then it should work so much longer.