The headline first: the same printer, the same nozzle, the same filament, and roughly double the usable speed once I moved off Marlin and onto Klipper. No new hardware beyond a Raspberry Pi I already had in a drawer. I had assumed my printer was simply a slow printer. It turned out it was a fast printer being held back by an 8-bit board doing trigonometry it had no business attempting.
what Klipper actually changes
Marlin runs everything on the printer's mainboard. That board is also responsible for stepping the motors thousands of times a second, and the two jobs fight. Klipper splits the work: the Pi does the heavy planning and kinematics, then streams precisely timed step commands to the microcontroller, which now does nothing clever and is much happier for it.
The practical upshot is that motion planning stops being the bottleneck. The board that used to stutter on dense curves just executes the schedule it's handed. My old "fine, but don't push it" speeds became my new normal.
the two features worth the faff
Input shaping was the one that made me sit up. You stick an accelerometer on the toolhead, run a test, and Klipper measures the resonant frequencies of your machine. Then it actively cancels them. Ringing and ghosting that I'd written off as "that's just what cheap printers look like" largely vanished.
[input_shaper]
shaper_freq_x: 52.8
shaper_type_x: mzv
shaper_freq_y: 41.6
shaper_type_y: mzv
Pressure advance was the other. It manages the lag between commanding extrusion and the plastic actually arriving, which is what makes corners bulge and seams blob. Tuned properly, the corners go crisp. Both of these are calibrations, not hardware, and both were sitting unused on my printer the entire time.
the honest part
It is not free. The config is a text file, and you will edit it more than you expect. The first evening was spent mapping pins and swearing gently at a MCU 'mcu' shutdown message that turned out to be a flashing fault on my end. The web interface via Mainsail is genuinely lovely once it's up, but getting up took a session.
Would I do it again? Immediately. I spent one evening and got a meaningfully faster, quieter, better-looking machine out the other side, with the added bonus that I now understand my printer instead of merely owning it. The drawer Pi has paid for itself several times over, which is more than I can say for most things in that drawer.