It’s not junk but it’s hard to hold steady for very long. Works best if you can lay your bud on a table and check it out that way. Nothing beats using a jewelers loupe.
https://www.rollitup.org/t/do-it-yourself-homemade-tds-calibration-solution.328966/
Thanks for your post. I didn’t know TDS meters could be calibrated. Found this and thought it would help.