If the pilot chooses to operate his or her aircraft in ground speed mini - or any other function - in order to comply with the ATC clearance I see no problem. If the controller wants the aircraft to fly at a particular airspeed for separation purposes I would expect the pilot to fly at that airspeed. If no specific airspeed is required, ground speed mini function seems fine. Any variations in airspeed resulting from the use of this function is unlikely to cause ATC difficulty else a specific speed would have been mentioned.
What would cause me concern is to specify an airspeed only to find that the aircraft is set up to fly at a particular groundspeed - the two are different.
To answer the original question (although I am no longer operational), in my day if I had not applied any speed control I probably would not noticed the variation in speed caused by ground speed mini function and it wouldn't cause a problem because the sequence wasn't tight enough to apply speed control. I should stress that I did not work a high-density environment and so was not routinely aiming for 3 miles - no more and no less - between aircraft. As Roffa points out, even small variations in speed difficult to accommodate in a sequence when the pressure is continually on to pack the aircraft as tightly as possible and the controllers are good at doing so.