How precise? The design precision is .3 pH. That is not as precise as even a very inexpensive meter.
As for accuracy, they measure .3 low at reference temperature, compared to a calibrated meter at reference temperature.
This isn't a temperature issue, they are just wrong in mash, for whatever reason.
So the pH meter makes an electronic correction for it's inaccuracy and you have to make a minor mental correction. After that correction they are both accurate. Besides, it's pretty easy to get a bad reading from a pH meter in complex solutions like a mash. Some pH meters don't handle ions as simple as sodium very well, let alone complex species like proteins. Two calibrated pH meters can easily differ by 0.3-0.6 when measuring the same solution. Don't be fooled into thinking that, just because you get a digital readout that you know the exact pH of the mash. You really have no idea if the pH is 5.3 when the meter says 5.3.
The strips will tell you that the mash pH is between 5.3 and 5.6. When the color is between those two spots you can assume it's closer to 5.4-5.5. I think that's an appropriate precision for brewing, which you may not.