I use Iris v2 3210-L outlets as my repeaters and have had very good luck with them. All of mine are up to date with the last firmware that was released for them. I actually bought an Iris hub early last year for ~$25 new from Lowes, in order to upgrade all of the firmware on these Iris devices. I figured I might only get one shot at it, before Iris was shut down. A SmartThings hub can be used to upgrade the firmware on Iris Motion and Contact sensors, but not the Iris outlets.
The only issue I believe may exist with the 3210-L outlets running older firmware is with the Z-Wave repeater side of things. Since you already have some of these outlets, if you turn them over, you'll find the main product label. If yours also have a small, white, rectangular barcode label, there is a very good chance that they are running the latest firmware.
