They need to test each unit better before recycling
930177
Sometimes the cartridges don't work--usually they do. But you get an ocassional dud--the circuitry or some other component is probably too worn to recycle sometimes.
2405848
I really liked the first one I bought, so I bought several others. That is when I realized that they had severe quality control issues. I fixed this by buying more than I needed and sending back the defective units. They have a leg in the back to stand it up and a magnet to attach it to metal. The ones I kept have worked well over the last year.
539677
This product has gotten progressively worse. Some of these filters are defective; brand new filters have particulate ratings between 100 and 120. I also fill them more than once to see if the particulate count stays the same and it does.

Also, the black filter particles that make up the filter process often float to the top; you have to particularly careful when filling the Zero water container not to let the water hit the circular area where the water drains into the filter.

I've been using this product for about a year.
2946150
Some batteries need to be tested 2-3 times to show an accurate reading. Works great if you are willing to do that.
435222
One filter was damaged. There was a felt pen marking where the damage had occurred. I believe the manufacturer attempted to grind out the defect when it should have been tossed out.
3007797
This battery tester fairly accurate.  I tested it on brand new batteries and used batteries, and  the "power level" will reflect the usage.

I have been saving money with this battery tester.  Here is how:

1.  Different item requires different level of battery power - Not all of electronic equipment need batteries at 100% good shape.  For example, my trashcan is battery operated.  Once those batteries hit to the "yellow" zone, the trashcan's  lid will no longer fully opened.  It's annoying, because the tester indicates that those batteries still have some juice left in them.  So what do I do?  I take those batteries and use it on LED flashlights.  Works perfect.  Those used batteries last for another 8 months before it's tested at the "red zone".  Some of you will say "you are not supposed to reuse an used battery".  You know what?  I don't care, that same flashlight works just fine.  With the amount of money I saved, I can easily buy another flashlight.  With that being said...you might want to think twice on this tactic for more expensive electronic equipment.  Flash lights, remote controls and some other indoor equipment works well with the used battery (in my experience at least).

2.  I have a bunch of batteries bought from Costco, some claimed to have 10 year shelf live and some claimed to have 5 year.  This battery test helps to make sure that I am not getting ripped off.  I did end up returning 1 pack of battery to Costco because the power level was just way too low for those batteries.

I have tested this with C battery but not D.  Can't give it a 5-star until I have tested on D.
3901848
Could be a fragile product if not handled with care.
4127163
We have bought two items and when we turned on the equipment the data seemed to be good but when the relative humidity when above 80% the data changed from each item, one 94% and the other 83% to much difference for 2 devices in the same place, we also saw the error test but the equipment is new, we will check this product with our electricity technician and also will need to calibrate the product but it appears that it was not calibrated from factory.
2029600
This is the 6th pack ive ordered from amazon and at least one nock on 4 of those packs was defective. Problem is... I keep a couple of packs in my case and don't open the packs until Im ready to use them so I don't find out they are bad until sometimes weeks or months later.

Very disappointed in the quality control.

@ nearly $9 a nock, you would assume there would be a substantial amount more quality control on these and that your product would have a lot better then 33% fail rate. I bought 3 packs of Clean-Shot Nock-Outs to compare. As you can see... all of theirs work. Can you help me? I am hoping that I just purchased from a couple of bad batches.
1789759
Unit was shipped with nearly dead batteries. (This company Lynxtech should include a plastic shield, like the kind you regularly find in battery-included products to prevent them from draining during shipping.) I removed the battery compartment to twist the batteries a bit, replaced into the unit and then was able to get 4 water tests done before the batteries died again. This is ridiculous that I have a brand-new item and *I* need to go buy new batteries, which will probably cost more than the $9.99 price of the unit itself. And, there isn't any indication on the unit to tell me which way the positive and negative parts of the battery should go.. Going to just hope for the best! However, when the unit was working, the tests were about as expected (tap water and filtered water from two different locations).
4241356
I ordered multiple units and before installing I tested each cable run before fishing it thru walls and floors. Every cable I tested passed.
3832563
This unit did not function properly.  I noticed it was starting to open up and upon closer inspection I noticed a internal plastic piece was broken and the broken piece was not in the case.  It's now in recycled garbage.  The VGA version is working fine.
2788395
The good ones do the job but quality control is lacking. Several of the male-male pieces had huge chunks taken out of the ends and one of the female-female pieces was covered in splinters. They also fit quite "loosely" with our Brio tracks which may be an issue if you use the battery operated trains.
1669933
Ive had to reorder this product twice due to defective parts that didn't allow for proper building. Unfortunately I don't have the time or energy to re order this product and try to rebuild again.
2741344
Found a large crack on the side of the unit when pulled out of the plastic bag.  The box was ok soooooo it had to happen at the factory. So much for QC. I had just un packed and put the box in the trash went in for coffee the trash was gone and then found the crack. Unit appears to work.
2 stars is for QC (what QC)  If you buy one inspect unit before you trash the box.
1642078
currently, my evaluation is poor, given how long it runs on two of the solid fuel components. I'll have to try natural source to see if that improves the performance.
4794698
Some of them were stale. Not sure if they were stored properly.