As far as drivers go today I think the best we can do is TMC2226 drivers. They are basically the same as tmc2209 but they run cooler under the same amount of load. The smoothers are for older style drivers that do not actually look at the current going out to the stepper motor. In order for features like sensorless homing or stallguard to work the driver very much needs a clean, low resistance, and direct path to the stepper. Because it is looking at the load and it can tell when a motor gets loaded to the point of skipping a step. Even without dedicated feedback wires. Just by looking at the current going to the stepper with ultra sensitivity. And so you should be able to see how putting banks of diodes, resistors, capacitors, or transistors might skew that driver's ability to perform it's job. And so those smoothers are really made for the older a4988 and drv8825 drivers that nobody uses. The tmc2226 drivers you can get right here: BIGTREETECH TMC2226 V1.0 Stepper Motor Driver – Biqu Equipment . They are cheaper than the 2209's also. Which is an added benefit. For smoothing here in 2021 we can look to software like arc welder to smooth things and reduce the overall amount of gcode using arc commands. Here is an informative youtube video on that: https://www.youtube.com/watch?v=18uYYXecH5g&t