I feel the best value is/was Aeon Labs DSC06106-ZWUS - Z-Wave Smart Energy Switch , which handles about 1450watts and 14+amps, unlike a lot of smaller plug-in modules. This is pretty big and the light is somewhat obnoxious. But holy cow, Amazon is presently showing $57 each and limited availability… so
I prefer plug-in modules to be less than $30. Pretty much anything will work. The one exception I know of, is Schlage RP200 Dimming Plug - I forget the exact behaviour now but it was persistently unreliable - it might have just been a single lemon.
I find the Zwave plug-in’s to be less annoying that the Zigbee plug-in’s.
All the plug-in’s will repeat so signal strength should improve as you add more.
The most convenient plug-in I have, is Remotec ZDS-110us, which can be manually switched between dimming and on/off-only. Plug spacing is not terrible (like some that block the lower plug on the wall receptacle). And provides an unswitched plug on the module. But the power rating is not great, something like 4-500 watts. I wonder if it’s rated higher for on/off-only - strange I don’t see them on the market now.
The GE/Jasco plug-in’s have been pretty reliable, now that I think about it, they also have an unswitched plug that is convenient.