I have tried many PH meters in the last 15+ years ( I do saltwater aquariums also). I have tried expensive ones, mid grade (blue lab) and many cheap ebay/amazon china pens.
Expensive ($300+) are very nice
Mid grade ones I was not a fan of for the value and maintenance.
Cheap ones are pretty much useless EXCEPT the Milwaukee Instruments Ph600 at around $25
I have been using this model for Aquarium, Hot Tub and Grow for a long time, probably 10 years now (I am on my second Ph600, i sold my last one with my old grow gear). I know there may be some not so good reviews on this model but I can tell you that it takes a lot to break it. its a single point calibration which makes it nice, though i keep both 7 and 4 solutions just to test the probe. I store in the 4.0 solution also ( no need to school me on this
)
I have left this thing without lid in the summer sun for 2 days, I have used RO water testing (yeah it kinda broke but it came back to life after a 4.0 soak, don't measure RO water folks!). I constantly let the probe dry out and the thing keeps chugging.
It does need to be checked before using most of the time as reviews say but I have found the calibration goes off a bit onlu if the lid is not put back on right away within minutes. Air seems to throw it off within 10 -15 minutes.
TDS meters are dirt cheap, i have been using my 10 dollar one since 2001. It was a chinese ebay item, works good and has temp as a bonus, but the Fahrenheit conversion math is really bad and off by 20 or so LOL (ironic?) so I only use the Celcius setting