Kingston has a few excellent encrypted flash drive solutions. Their flash drives are always high-quality and are known for their reliability.
Kingston DataTraveler Vault Privacy 3.0
Their basic encrypted flash drive. (~$60 for 16GB)
encryption certified by FIPS 197 standard
optional antivirus (I can't attest to the usefulness of this)
After some poking around, the closest I came to meeting your question's requirements was this: Black Aluminum MicroSD USB Card Reader works with all sizes TF card capacities.
Meets most of your requirements:
Fixed USB A connector
Works as a micro-sd adapter/flashdrive
Intended to be used for keyring-carry
Doesn't quite meet these requirements:
Corsair CMFSL3X2-128GB 128GB Voyager is one I use myself, it's an extremely compact design, 128gb and has 90mb/s write speed, which seems to fit your specifications, however, I'm not sure about how strong the key ring attachment is, I've had this for three years now and I've had no issues so far, so I guess unless you are handling it roughly, I don't see why ...
It seems there are no USB sticks with hardware write switch of such small form-factor as Kingston SE9 (39mm of length). There are some alternatives smaller (shorter) than Kanguru SS3.
Kanguru FlashBlu30 - 64mm (8-64GB) / 71mm (128-256GB)
Netac U336 - 67.5mm
Kanguru Defender 3000 - 72.2mm
Kanguru SS3 is long 77mm
searching for a small SD ...
I created the question but I cannot modify it nor comment.
Thanks for the comment, but the drive has to be non-volatile.
Can you please modify the question as follows (and then fix this into a comment)?:
Context: I want to store data in digital format, and then destroy it. Let for the moment put physical destruction of the drive (hammer/degausser) aside.
This one says its 2" by 1.2"
Caution 15 of 46 customers units reviewed on amazon failed.
43% had no reported issues. However, 46 reviews is hardly statically significant.
Naztech makes a device they call the "Xtra Drive Mini" that is something like what I am after:
It's made of aluminum, takes a microSD card, and attaches to a keyring. It has shortcomings though:
Non-retractable (read: easily broken) proprietary Lighting connector
with a removable (therefore loseable) cap.
No keyring hole like the DataTraveler or Samsung ...
So essentially, what you would want is an Arduino pro micro with a usb adapter. Seytonic on YouTube did a whole series about a DIY rubber ducky using an Arduino. you can find his first video on the subject here but once you have seen said video I recommend watching the updated video on the subject which you can find here. He also goes deeper by adding on ...