I bought a $7 off eBay, been using it for 6 months, and it's as fast and accurate now as when it was new. I set it up with 7pH buffer and when I check it with the pH4 solution it was spot on. I only bought the pH7 buffer to double check the powdered buffers, which are rated at pH6.86
However after getting to know the indicator solution having used it for a long time, and using my experience in fine colour correcting, I can confidently say that the indicator solution if you know how to read it, is at least as accurate and in fact more accurate in the sense that if I get a strange colour I'll be worried, but if I got a strange reading on the pen, more than likely I'd double check it against the indicator solution.
The indicator solution is only accurate between 5.5 and 6.5 and it's most accurate between 5.8 and 6.2, again, if you know how to read it. I use one drop of indicator in a tube with 2 or 3ml of nutrient.
pH6 is a neutral yellow
pH6.2 has a hint of green in the yellow
pH5.8 has a hint of red in the yellow.
It does take some practice and it's good to use a pen that is accurate to set it all up and be confident you are correct. These days to check how well I can judge it, I just mix up some water buffered down to pH3, then I keep adding masses of tap water and try and see how few samples I need to take to get it to exactly 6.
The indicator solution is as accurate as is needed to grow dope, and the most sophisticated dope growing facility in the world could easily just use indicator solution to check their nutrient pH and it would not make any difference.
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I’d never heard that I always thought you slipped the cover back on and stored it away. So I take it you mean the probe tip should always be submerged in liquid(tap water or “ kcl probe storage solution?”while not in use? That would be kind of tough for my yellow cheap one to have only the tip submerged in tap without the whole thing submerged. Unless I like tied a string to one end and hung it above a glass of water or something.
I store my cheap $7 yellow meter without the lid, in a glass with the bottom one inch filled with unused or used ph6.86 buffer. It makes it much faster to take a pH reading when the pen is stored this way.
Keep dreaming!