MMD KM21 Ultra vs MelGeek O2
Choose the MMD KM21 Ultra for four clickable knobs, QMK/VIA and hot-swappable switches, or the MelGeek O2 for its larger 2500mAh battery, PBT keycaps and adjustable typing angle.
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from$89at MonacoKeys
from$109at MelGeek
90-day lowLowest price in 90 days
Which one should you get?
Get the
MMD KM21 Ultra
Hot-swappable
Build quality in the top 15% of Numpad boards under $100.
- Four clickable, configurable rotary knobs provide extra physical controls.
- Hot-swap sockets allow solder-free switch changes.
- QMK and VIA support enable key and knob remapping.
Get the
MelGeek O2
Battery
Build quality in the top 50% of Numpad boards under $150.
- A 2500mAh battery offers greater listed capacity.
- PBT keycaps and a polycarbonate plate are specified.
- Adjustable typing angles are described by the vendor.
- Switches are soldered. Swapping them means soldering.
- North-facing LEDs. Cherry-profile keycaps can hit the switch housing.
Get the MMD KM21 Ultra for its four clickable knobs, QMK/VIA configuration and solder-free switch swapping. Choose the MelGeek O2 for its 2500mAh battery, PBT keycaps and adjustable typing angle, while keeping its soldered switches and north-facing LED compatibility in mind.
The differences that matter
Skip the 40-row spec sheet. These are the specs that change how each board feels, sounds, and fits your desk.
MMD KM21 Ultra
MelGeek O2
Hot-swappable
Yes
No
Switch changes without soldering
Battery
980 mAh
2,500 mAh
A larger battery means fewer cables during the day
Case material
Aluminum
ABS, Aluminum, Polycarbonate
Mount style
Top Mount
Gasket Mount
Knob
Yes
No
- MMD KM21 Ultra
- MelGeek O2
- Performance
- 6654
- Build quality
- 8165
- Productivity
- 8953
- Customizability
- 8950
- Portability
- 8582
- Layout size: Numpad
- Connection: Bluetooth, 2.4 GHz, Wired
- Sound dampening
What will you mostly use it for?
The KM21 Ultra leads for workflows that benefit from programmable inputs, physical knobs or switch changes without soldering. Its four clickable controls make it particularly suited to creative shortcuts and custom command setups. The O2 is the more compelling travel pick based on its larger battery and listed weight and dimensions. Both have wireless and wired connectivity, so those options do not decide the comparison.
Pick the MMD KM21 Ultra
- The KM21 Ultra has four clickable knobs and QMK/VIA support for configurable controls.
- Its hot-swap sockets allow switches to be changed without soldering.
MMD KM21 Ultra vs MelGeek O2 specs
Every tracked spec, side by side. Rows marked with a dot differ between the boards.
11 of 23 specs differ
MMD KM21 Ultra
MelGeek O2
Hot-swappable
Mount style
Sound dampening
Layout size
Layout standard
Ergonomics
Knob
Display
Connection
Max polling rate
Battery
USB-C
Case material
Plate material
Keycaps
Weight
Dimensions
Typing angle
Backlight
QMK
VIA
Mac & Windows
Released
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MMD KM21 Ultra vs MelGeek O2: your questions
The KM21 Ultra focuses on customization, with four clickable knobs, QMK/VIA support and hot-swap sockets. The O2 lists a 2500mAh battery, PBT keycaps and adjustable typing angles.
Yes. Its four knobs are clickable and the vendor says they can be freely assigned through VIA. The vendor describes uses including volume, zoom and timeline scrubbing.
No. The O2's switches are soldered, so changing them requires soldering. The KM21 Ultra has hot-swap sockets for solder-free switch changes.
Its north-facing LEDs can cause Cherry-profile keycaps to hit the switch housing. Buyers planning to use that profile should account for this compatibility constraint.
The MelGeek O2 lists a 2500mAh battery, while the MMD KM21 Ultra lists 980mAh. Capacity alone does not establish actual battery life for either device.
Yes. The KM21 Ultra lists QMK and VIA support, and the vendor says its keys and knobs can be configured through VIA. The O2 listing names MelGeek Hive instead.
The KM21 Ultra has four clickable knobs, with the vendor describing uses such as timeline scrubbing, zoom and parameter control. Its QMK/VIA support also lets users configure those controls.
Both list Bluetooth and 2.4 GHz wireless, as well as wired connectivity. The KM21 Ultra vendor description specifically names USB-C, 2.4 GHz and Bluetooth 5.0.
The KM21 Ultra has hot-swap sockets, allowing switches to be changed without soldering. The O2 uses soldered switches, so a switch change requires soldering.
The O2 product description specifies MIA custom-height PBT dye-sublimated keycaps. Its north-facing LEDs may affect compatibility with Cherry-profile replacements.
The vendor describes the O2 as having adjustable angles. Its specifications also list an approximate 3.5° typing angle, or about 5° with the feet.
Choose the KM21 Ultra if you want to change switches without soldering, since it has hot-swap sockets. The O2's switches are soldered, so changing them requires soldering.
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