I'm a big fan of the SonOff and also the tiny Tuya Zigbee repeaters (which are much easier to hide than the SonOff). 
You probably know, but you'll need to flash the SonOff after they arrive - info on that here.
I'm using a mixture of SonOff, Iris/Centralite, Ikea, Tuya, & Sengled repeaters on my two hubs.