The RC Komatsu PC400LC is based on an old model which makes it slightly harder to get, I was lucky enough to get one second hand on ebay at a reasonable price. You can tell straight away the quality of this model from how smooth the slewing motion is. The ROS Hitachi model has a lot of friction in the slew motion where as the Joal Komatsu glides around. It is also screwed together slightly better as there is much less plastic in the construction.
It still suffers from the weight issue of the Hitachi, the boom is very heavy but with the new screw mechanism design this should be no problem. The screw mechanisms are based on M3 threaded bar with an N20 gear motor to drive each screw.