I had a milwaukee.
Out of the box it worked well. But after about 6 months, I would calibrate it with 4dkh and 7dkh solutions and then compare it against a liquid test kit and they never compared! They werent even close. My only thought was that if the liquid kit (I used multiple kits and they all agreed with each other) was that far off, there are thousands of people with ph problems in their tanks. So I came to the conclusion that the meter was off even though it calibrated well.
That led me to decide that the probe was bad and i wasnt ready to fork over roughly $50 for a new one after only 6 months.
Then the next conclusion was that if it was that far off, then my CO2 level was also off, so I just stopped using it. It wasnt worth the trouble.