Most DC motors of that "windscreen wiper" sort are brush motors. I am not sure about the one in the Amazon link. It is true that stepper motors have distinct "steps" between magnet poles when you turn the shaft by hand. Electronic driven, a common step was 1.8°, If delivered fast enough, and the motor geared down, it looks like a smooth movement.
The guys who do CNC conversions will, by now, have a huge store of knowledge about using small motors to drive power feeds. There is a class of small DC servo-motors that have a tiny tacho-feedback generator on the back, for speed control with full torque.
This is where we get to the way motors work. If you limit the voltage to the motor, it will go slower, whether the method is to lose the volts as heat in a resistance, or to (more efficiently), feed it a pulsed voltage with variable "on" durations with a PWM speed controller. The other reason it would go slower is when the load varies. The way you get a constant set speed feed is to measure the speed, with feedback, and have electronics to respond appropriately.
Now, with small AC motors, they can be driven by servo electronics clever enough to sense the coil currents, and figure out the speed. We call them VFD's, although now, what they do has come a long way from simplistic frequency variation. For all this, I do allow the motor costs some, and additionally, the controller costs some more.
If the torque from the Makermotor is enough to turn your mill feed, and you can contrive a 12V supply for 5Amps, then what is left is feed rate control. The dilemma is that if you turn down the speed with your non-servo voltage control, you also turn down the torque. At zero speed, it acts like a stalled motor, and will take a very high current until the rotor moves. You get the "lurch" as it gets going, then it revs up to way beyond the speed you would need, and you have to dial it back. Only with a very geared down drive, can you just switch on, and have it come up to a preset speed.
I think you might ask among the CNC guys, what is a satisfactory nice straightforward controlled motor arrangement to turn a mill feed. By now, they will already have made all the mistakes, and will likely know.