Most of these new smart meters are programmed not to give a credit for energy returned to grid. That can be a problem with underloaded reactive loads like electric motors used in poop pumps, compressors, etc, that may return some power back to grid.
I suspect the net over billing could be several percent, maybe more.
Additionally these meters are not suitable for grid tied PV installations..
Second, nearly all of them have remote power interruption capability. So your power can be remotely interrupted at any time, by the power co or by some hackers(it's just a matter of time). And your neighbors will be none the wiser unless they go inside your house or notice something odd.
This could easily inflict major losses on the electricity consumer. Spoiled food, disabled alarm system, toxic conditions in an aquarium, or worse.
Thirdly, unlike mechanical meters where the mass of the disk act likes low pass filter, these smart meters can be susceptible to RFI generated by the load, this could result in gross billing errors. Note: There is no way to real way to test for these types of problems in advance.
So far, I've manage to refuse the installation of one of these smart meters..
But my luck may run out, soon or later.