I used the first one that came into the UK, and later bought one.
The recoil is different to the RM4's as it's felt on the top rail, not into the buffer tube. On an 11.1v Li-Po they are insane and bring a real grin.
I would recommend replacing the hop rubber, the KWA ones are for US fields - not UK ones.
Also, ensure that it has a UK compliant spring in - most directly imported guns from the US - via the wholesalers will be over UK power limits.
For the full run down, pop over to the KWA ERG user group on Facebook - https://www.facebook.com/groups/778600538840596