Final summary with probably a lot of wrong information I was able to compile in my head, written here for the future troubled users
sdparm technique I saw in tutorials was used mainly to somehow trigger mode-changing in USB devices. I don't understand this, but apparently there are a bunch of USB devices that are detected in one way and then if you eject them or send some other command it will have its mode changed (each one has its own specific set of commands that will trigger that mode change, see
/etc/usb-mode.json for a list of devices and their spec, that list is built from the collection of devices at http://www.draisberghof.de/usb_modeswitch/ and apparently not used only in OpenWrt, but in other linuxes also).
Maybe it is because of that that
eject were removed (although this last one seems to have a comeback planned). If your device is listed in
/etc/usb-mode.json and you have
usb_modeswitch installed it will be automatically ejected (or triggered with its specific command) and you'll never have to manually call
eject -- or you can manually call
usbmode -s and if it's there on the list it will be triggered.
The list identifies devices using pairs or
idVendor:idProduct, which are supposed to be the same for devices of the same model. You can list all devices along with their ids by calling
My device wasn't on the list. Apparently all devices in the world are on the list, so no one knows what to do when they aren't, except for bmork, who helped me in this thread: 3g/4g USB dongle not showing up