some of thoose meter are notorious for sometime giving incurate result.
As I wrote, they don't need to be accurate. They only need to be reliable. Remember, the readings are being compared against previous readings using the same device. So, the device can be wrong if it's wrong the same every time it's used.
also diging holes each time may damage the roots ,
It's not actually digging, but worth keeping in mind, nevertheless. So, don't force the probe into the soil and avoid areas where the roots are most concentrated, i.e., the root ball.
plus you need to check the humidity at different location inside the pot near the top, bottom, middle, side ... ...
Good point. It's a distinct advantage of using a probe. Such granularity of information isn't available when lifting a pot. So, I recommend checking different locations if there's an issue. Most of the time, when the plant is growing well, a single insertion is adequate. I also usually don't check if the plant was recently watered. After a few grows, most of us get a "feeling" for such things as when to check if the plant needs water.
Usually, I check near the sides of the pot, or about halfway between the stem and the side. That's for a fabric pot. Plastic pots would be different, I suppose, but I don't use those so I can't comment from experience. I don't probe the root ball directly under the plant unless I'm trying to diagnose a problem. When I've done so, it usually tests moister there.