Just had a look at the Energenie Products and website etc.
So wish these were Z-Wave 
From what I can see and correct me if I am wrong is the following states its one way, and can only send the signal to command the device and thus its stateless, a super quick browse and I cant see any of the retrofit Items (Light Switch and Sockets) as having anything other that one way
Radio Frequency 433.92Mhz
-Data Protocol Simplex one way, OOK
- Receiving Range 25 meters in open area
- Encoding 20 address bits (preset OTP), 4 data bits
- Socket Rating 220 - 250V~ 50Hz, 13A, 3000W max. each socket
Not sure what the OOK is however, but if in fact they are stateless, then its no different to LightwaveRF which are also stateless and a bit cheaper I think too.
@adamclark_dev has already created a great setup to allow UDP control of LWRF via Smartthings.
Lightwave /SmartThings integration
Anyway I hope I am wrong and they are stated and then if they did integrate then it would be a great solution for the UK market. Given we lack so much device diversity here.
Until then for me its Re-Tractive Switches with Aoen Micro Switches and LWRF Retrofit Switches and Sockets.