One more thing regarding these outlets... there are two different firmware versions for the 3210-L outlets. The early firmware was known to have issues with the Z-wave repeater side of things. I believe those issues were resolved in the new firmware for these devices, but I am not 100% certain.
Unfortunately, there is no longer any way to update the firmware on these devices that I know of. One way to determine the firmware version is to pair the device with a SmartThings hub and then look at the device details in the ST Web IDE. ST can update the firmware on Iris v2 Motion and Contact sensors, but not these outlets.
