An RO review written the week of installation mostly tells you how good the manual was. The real differences between models show up later: at the first cartridge change, at the first fitting that weeps, at the moment you try to find a compatible membrane three years after buying. This section collects my detailed reviews, and I will start by handing you the checklist I use, so you can judge any product page yourself.
My evaluation checklist
The before-and-after measurement. A serious RO review quotes numbers: TDS (total dissolved solids) in and out, measured with a $15 meter. A healthy membrane holds back more than 90% of dissolved solids. "The water tastes better" is not data, it is an impression.
Fitting quality. Leaks are the number one failure on under-sink systems, and they come down to details: well-machined quick-connects, tubing that seats firmly, locking clips included. That is typically what separates an iSpring from a bargain unit, and no spec sheet mentions it.
Whether consumables are findable. I check that prefilters and membrane can be bought away from the manufacturer's own store, in the standard 10-inch format. That criterion decides the real service life of the machine, as I explain in my comparison method.
How the tank behaves over time. Air pressure that holds, a bladder that does not tire, a flow at the dedicated faucet that stays decent — none of it can be judged in less than months.
Where I stand on honesty
None of the systems in my selection has run under my sink long-term: I have one kitchen and it is already busy. My reviews cross-check verifiable specifications, long-run user feedback (reviews updated after a year are worth their weight in gold) and my own experience of maintenance and TDS measurement. When a point cannot be verified, I say so. The models I talk about are introduced on the section's front page, and the choice between RO and simple filtration is settled in reverse osmosis vs pitcher filter.
