I will answer my own question.
I ended up buying a SanDisk extreme plus micro SDHC 16 GB (20€).
OSMC runs more than smoothly on it.
16 GB seems to be a good size. OSMC takes less than 300 MB but the metadata, thumbnails, artworks and add-ons are also stored on the SD card.
I'm able to play my heaviest movies (20 GB) through NFS without issue.
Any card ...
I recommend using a SanDisk MicroSD card. They're probably one of the most popular options, and for a good reason, too. They're very reliable, and not too expensive (Especially the 64GB one; The 128GB is newer technology, so it'll cost more per GB). I've used mine for years, and never had any problems with them.
It might be tempting to buy a really cheap ...
There are several great brands that make Micro SD cards, including, but not limited to
I read here that Samsung and SanDisk tend to make the best micro SD cards in terms of performance, but the difference is not much to look into.
Realistically, they will all serve you well, so if you do find a really good deal on a ...
SanDisk Sansa Clip+
$50 for 4gb and $100 for 8gb anyway both have SDcard slot.
MicroSD card slot.
Robust file support.
FM radio and recording.
Rechargeable battery lasts up to 15 hours.
MP3, WMA, Secure WMA, FLAC.
I tried it before the sound quality really good.
Edit: The maximum Memory size MicroSD card is 16GB according to this article
Or Sandisk Fuze
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:
Cards which are working perfectly:
SanDisk Ultra 64GB
Kingston microSD-XC 64GB UHS-I U1 GOLD Class10 SDCA10/64GB + adapter (90/45 MBps)
Another cards (although they are only 32GB ones) which also work well:
Kingston microSD-HC card 32GB ULTRA Class10 SDCA10/32GB
Samsung Memory 32GB Evo MicroSDHC UHS-I Grade 1 Class 10 Memory Card without Adapter
At this moment there is no phone or tablet which supports UHS-II. Of course you can put UHS-II card in normal slot because it's backward compatible but there is many opinions that this cards are working worse than UHS-I cards when they are in UHS-I slots.
I have personally used an Arduino with a GPS module an SD Card module to plot GPS coordinates. This is a bit of a DIY project and requires some programming, but given your StackOverflow reputation this should not be an issue for you at all and has the added benefit of being customisable to your exact needs.
The Arduino can be powered using a powerbank which, ...
You could use multiple adapters
Now you have a device with ...
I can just say about my device and can fully remommend it to your needs:
SanDisk Sansa Fuze V2 with rockbox firmware -- no touch screen, so no "unlocking"-problem at all, small, with rockbox about 20hrs battery life continuos play. The Wiki Page on rockbox.org seems to have quite outdated information, but in the last year or two there was new active ...
Finally, I've found the right device. It's Fiio X5 3gen. It handles playing files in big folders (10000+ files) without any delay even if the random mode is on.
It has all features I wanted, sometimes it's even more than I expected (two card slots).
The only disadvantage I've found so far is that the device is quite big (it's a lot thicker than average ...
I would go with the following: FiiO X1 High Resolution Digital Lossless Media Player
Professional quality Texas Instrument PCM5142 DAC and Intersil ISL28291 OP amp
Bright and easy to read 2" color LCD display. Custom user interface with color themes
Durable lightweight aluminum chassis, metallic buttons with concentric grooves, scroll wheel of textured ...
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 ...
Kingston Digital USB 3.0 Super Speed Multi-Card Reader for SD/SDHC/SDXC/microSD/MS/Compact Flash CF Cards (FCR-HS4)
Manufacturer page: https://www.kingston.com/US/flash/readers/FCR-HS4
Amazon page: https://www.amazon.com/gp/product/B00VAGX6MW
Meets all your requirements and I have used it successfully with Linux Kernels beginning with 4.4, 4.8, 4.10, and ...