I remember reading a thread about this particular weapon at HKPRO two or three years ago. According to a Mexican poster, the FX-05 wasn't particularly successful and the mexican government continued buying G36s instead of relying on a domestically produced gun. I don't know if this is true at all but we mostly only
see these guns at parades although recently they seem to popping in the hands of counter narco type units. It seems that Mexicans are still employing licensed built HK G3s, M16s and HK G36s as their primary infantry or police arms. This seems to suggest that the Mexicans either don't have enough money to replace all their
arms at once or the FX-05 is experiencing issues precluding it from wide scale adoption. Also, HK might have forced them to stop production. As far as similarity to the G36, I have gleaned that the receiver is very similar to the HK but the operating system employs a long-stroke Kalashnikov type gas system instead of the
AR-18 type short stroke. There appears to be some good innovations in this gun like the nice beefy adjustable stock and a rail molded right into the receiver rather than the goofy carry handle thing on the G36. The biggest issue with this system is the fact that there is very little verifiable information coming from Mexico about it.