KWA is the way to go. The price difference isn't large enough to justify the switch to WE, and you will find that just browsing the classifieds there are a plethora of mp7's, parts, and magazines on sale.
Here's a reference review video from Khan-Seb of the WE smg8 that completely deterred me from any interest.
(Airsoft) Unboxing the SMG-8 WE and MK23 Marui (French with English subtitles) - KhanSeb - YouTube