Both units are modern high precision, isolated output, monopolar electrosurgical generators. Despite their different appearances, the MC-4A is literally two-thirds of the Radiosurge MC6A from an electronic perspective. The MC-4A lacks the pure CUT function of the Radiosurge MC6A.
Prosthodontics with its high precision sculptural aspects is the forte of the Radiosurge MC6A. Implant exposure and biopsy are not recommended for the MC-4A, however, for all other indications, both units are identical and share the same accessories.
In other words, the Radiosurge MC6A can address all dental electrosurgical indications whereas the MC-4A cannot. For general restorative dentistry there may be a bit of a dilemma which hinges on how much crown and bridge work is part of the practice : crown and bridge is better served by the Radiosurge MC6A as is all anterior aesthetically significant intervention.