@update
OK - just following this up with extra info.
Previously, I was using radios without the cap.
Once a 47 uf cap was added, I didn't need the extra power supplies (the USB power was enough to the Uno clones).
Thinking about this now, It wasn't the uno boards, it must have been noise/weak power on my laptop USB.

Also, I wasted a lot of time on a bad rf24L01 board ( I think I bust it a while ago by supplying 5v :( ).
So, the moral of the story?

• If you get a message saying "radio bad" - try another rf24l01
• ALWAYS add a capacitor to every rf2401 board

SUCCESS! - My "ESP8266 MQTT gateway" sketch now works OK - no need for a 3rd device :) :)
*EDIT I've been using this board and the problem is ....

I'M USING THE BOARD PICTURED BELOW AND THE LABELS FOR GPIO4 and GPIO5 ARE THE WRONG WAY ROUND (screen print error)

I swapped the cable from the header pin marked GPIO4 to GPIO5 and everything worked fine. I'm wondering if this is the same solution for a lot of people here (I've put this info on build page)
https://github.com/esp8266/Arduino/issues/437
https://twitter.com/bdcatalin/status/663434209265078272

Hope it helps someone

@TON-RIJNAARD
To test things, you need

1. Device 1 with rf24L01+ radio

• Load "gatewayserial" sketch

2. Device 2 with rf24l01+ radio

• Load motion sketch, but add a line before
  #include <MySensors.h>
  so that it looks like this
  #define MY_NODE_ID 1
  #include <MySensors.h>

Switch on both devices and look at the serial messages from Device 1 (Gateway), When movement is detected, you will see new messages etc