We've received an adapter from Lezyne (Japanese bicycle parts manufacturer) for mounting pedaling monitor cycle computers to

Garmin-compatible mounts.
Strictly speaking, this is our second shipment. The first batch sold out immediately.
The MSRP is 1,500 yen before tax.

↑Mount side

↑Device side

↑Mounted state

↑This is Garmin's OEM mount, but

it can be mounted like this. However,

mounting to mounts other than Lezyne
is not covered by warranty, so please be aware.
Garmin mounts have two prongs, but
"Garmin-compatible" mounts can have four prongs.
You can modify four prongs down to two, but not the other way around.

Whether two or four prongs (the image above shows four),
the adapter is secured by the ribs in two horizontal locations,
and the height and shape of these ribs determine the click feel during mounting
and the security after mounting.
K-EDGE and FAR AND NEAR aluminum two-prong mounts have
somewhat weak click and retention feel, so we don't recommend them.
In fact, they're specified as "unusable with anything other than Lezyne."

This shows a Yupiteru (Japanese GPS navigation device) handheld GPS
with a Lezyne heavy-duty double-sided tape four-prong adapter
mounted on the back.
You could also mount this on the back of a smartphone hard case
and use it as a cycle computer for a stationary trainer.
Of the four slot-shaped holes, two engage with the ribs on the mount side.

↑This is a four-prong mount.
The two-prong adapter also fits, more or less.

On a personal note, I normally use my Yupiteru not as a handheld GPS, but as
an ANT+ cycle computer
mounted on my dedicated three-roller trainer bike.

Garmin-compatible mounts.
Strictly speaking, this is our second shipment. The first batch sold out immediately.
The MSRP is 1,500 yen before tax.

↑Mount side

↑Device side

↑Mounted state

↑This is Garmin's OEM mount, but

it can be mounted like this. However,

mounting to mounts other than Lezyne
is not covered by warranty, so please be aware.
Garmin mounts have two prongs, but
"Garmin-compatible" mounts can have four prongs.
You can modify four prongs down to two, but not the other way around.

Whether two or four prongs (the image above shows four),
the adapter is secured by the ribs in two horizontal locations,
and the height and shape of these ribs determine the click feel during mounting
and the security after mounting.
K-EDGE and FAR AND NEAR aluminum two-prong mounts have
somewhat weak click and retention feel, so we don't recommend them.
In fact, they're specified as "unusable with anything other than Lezyne."

This shows a Yupiteru (Japanese GPS navigation device) handheld GPS
with a Lezyne heavy-duty double-sided tape four-prong adapter
mounted on the back.
You could also mount this on the back of a smartphone hard case
and use it as a cycle computer for a stationary trainer.
Of the four slot-shaped holes, two engage with the ribs on the mount side.

↑This is a four-prong mount.
The two-prong adapter also fits, more or less.

On a personal note, I normally use my Yupiteru not as a handheld GPS, but as
an ANT+ cycle computer
mounted on my dedicated three-roller trainer bike.