If you have a C8 and you want to add more Zigbee repeaters, I (and others) have found the SonOff USB Dongle Plus to be a very strong/active repeaters on the C8. Not as much on the C7. It does take a little work (you have to flash a different FW on them) but once set up they are really active repeaters for the C8.
Other Zigbee repeaters could include Third Reality plugs, Centralite Plugs, the tiny Tuya USB Zigbee repeaters, & Innr 224 plugs.
