Most of the Mitsumi based are 720k read compatible, none are guaranteed to write or format a blank 720k though.
The best ones I have are: Sony 2xFDD mpf88e, MacAlly FDD-USB d353fue (mitsumi based) and Generic FD-05pub (Mitsumi 061M based)
All the Dell branded ones I own will not even read a 720k floppy 🙁 Added: they are all NEC based

Keep on mind that floppy drives were slow, and although some USB disk drives offer some kind of "acceleration" you won't get anything remotely near "pendrive speed".

I guess the differences between brands are durability and the ability to read/write 720k disks. On the other side, the worst part is that no USB floppy drive is capable of reading/writing disks that aren't standard (80 tracks, 9 or 18 sectors per track, sector numbering starting at 0). So you won't be able to read 2M formatted disks, the Windows 95 or OS2 install disks, some copy protected disks or disks formatted in non-PC computers like ZX Spectrum or Amstrad CPC (although they can be read on standard floppy controllers).

Depending on your budget, you may want to consider a Kryoflux USB adapter along with a "real" 34-pin floppy drive . You would need to setup a workflow to convert to or from the native Kryoflux low level image format after reading (to make an img file) or before writing (so your source img file can be written using the Kryoflux compatible writing tool). My understanding may be based on dated info, so things might be easier now (I have not purchased a Kryoflux yet, but did consider one at some point and may yet get one).

See these for more info
KryoFlux to image floppies?

https://forum.kryoflux.com/viewtopic.php?t=1205

Additionally, if using a Gotek type device on your retro machines is possible for your use cases, it may be a convenient thing to consider as well (whether using a Kryoflux or not).

I think the IBM(Lenovo) ones are pretty solid. Do a search on you-know-where for 'ibm floppy usb'. Should get a few hits.
For instance number 303930810330 or 384053760104.

PS: I have no idea if they play nice with 720kb disks though, as I don't have any.

Thanks for the replies!
I didn't realise the inability to write/format 720kb disks was a common thing.
Anyway I've just ordered an IBM branded one.. let's see if this is any better (well it couldn't be much worse haha)

For anyone buying a new USB floppy available now on the market, a current model, my experience is that if they don't explicitly mention DD/720KB compatibility they don't have it.

Samsung SFD-321U/HP

most reliable fdd, support 720kb DD as well, I'm use it to write floppies for my Sony MSX2

Imation "Superdisk" (LS-120) drives. The packaging says they're for Mac but they also work on PC. Most require a chunky dongle thing to connect to USB, some of the late ones have a regular USB connector on them though.
The colored ones are older, slower, not as good at reading bad disks. The silvery translucent looking ones have better drives inside and can read disks you thought were hopeless. I'm sure there's some overlap on the cosmetics there but mostly that's correct.
A few years ago these were all over eBay, don't know if they still are.

If you hate slipstreaming WinXP install CDs, there's a limited list of USB floppy drives that they support unedited. There's a list floating around here somewhere.

shamino wrote on 2021-03-24, 15:30:

Imation "Superdisk" (LS-120) drives. The packaging says they're for Mac but they also work on PC. Most require a chunky dongle thing to connect to USB, some of the late ones have a regular USB connector on them though.
The colored ones are older, slower, not as good at reading bad disks. The silvery translucent looking ones have better drives inside and can read disks you thought were hopeless. I'm sure there's some overlap on the cosmetics there but mostly that's correct.
A few years ago these were all over eBay, don't know if they still are.

That's a good idea - I've never owned an LS-120 so I might set up an eBay alert 😀

Stiletto wrote on 2021-03-25, 21:04:

If you hate slipstreaming WinXP install CDs, there's a limited list of USB floppy drives that they support unedited. There's a list floating around here somewhere.

Here is an optional method for that, just edit a particular file (txtsetup.oem) found in the driver directory (and copy all files to the floppy):
(AHCI driver files for winXP on Z77 chipset)

1Utilizing a USB Floppy to Install an Operating System
2 ( Intel Article ID000007974, Last Reviewed11/01/2017 )
3Windows* by default does not have drivers for all USB floppies. When utilizing a floppy for adding RAID drivers, you may notice that the driver is loaded once. Later during installation, the operating system re-requests the file, but fails to find the floppy drive on the second attempt. If you are loading additional drivers during installation, there will be a file on the floppy called txtsetup.oem. Open the file on another machine using a text editor such as Notepad, and add the following lines to the bottom of the [HardwareIds.scsi.(device name)] section
4
5id = "USB\VID_03F0&PID_2001", "usbstor"
6id = "USB\VID_054C&PID_002C", "usbstor"
7id = "USB\VID_057B&PID_0001", "usbstor"
8id = "USB\VID_0644&PID_0000", "usbstor"
9This tells the operating system to use the standard USB storage driver for these additional floppy devices. You may need to contact your USB drive vendor to obtain their Vendor ID (VID) and Product ID (PID) if these lines do not resolve the issue.

...and my IBM floppy drive had this id below:
"USB\VID_0644&PID_0000"

PS: you apparantly have to edit 2 sections for this particular AHCI driver, not just one:

I use "Y-E Data USB-FDC" (as they appear in device manager) floppy drives, they support both 720 and 1.44 floppies and are faster than regular drives too. You can even hear them spin faster. I have one that is Toshiba branded and just today got two that are Fujitsu branded (of one will find a new home at some friend's place).

My IBM one just turned up and works great! Formatted a disk at 720KB too!

Almost identical case (just the blue eject button and two screws instead of one) to my rubbish old cheap one.

Oh it actually says TEAC Model No FD-05PUB on the bottom. Even came in a padded pouch 😀;

Glad to hear it all worked out !

And, checking one of my drives, a Lenovo version, what do you know - it also says 'Teac' somewhere on the paper label ! 😋
(an 'FD-05PUB' model, just like yours, but with a 'lenovo' branding and logo...)

So, I guess mine would also format 720kb disks then, if I for some inexplicable reason ever needed it to.... 😆

I've a slim Iomega unit (BXXU0130) which is a piece of junk 🙁 - no idea what brand the actual drive is

Tiido wrote on 2021-03-26, 14:06:

I use "Y-E Data USB-FDC" (as they appear in device manager) floppy drives, they support both 720 and 1.44 floppies and are faster than regular drives too. You can even hear them spin faster. I have one that is Toshiba branded and just today got two that are Fujitsu branded (of one will find a new home at some friend's place).

SteveC wrote on 2021-03-26, 14:41:

Oh it actually says TEAC Model No FD-05PUB on the bottom. Even came in a padded pouch 😀;

Thanks ! will add them to my list of good USB floppy drives.

PC Hoarder Patrol wrote on 2021-03-29, 01:45:

I've a slim Iomega unit (BXXU0130) which is a piece of junk 🙁 - no idea what brand the actual drive is

Thanks, will not add that model to my list 😀

I've been using dell laptop internal floppy drives, the ones that have a USB Mini-B connector on the side. They seem to work with whatever I put in them (though I don't imagine non-PC disks would work) and seem very reliable.

I got a box of like 20 of them NOS for free at one point and I'm kicking myself for only keeping one since I know now how nice they are.

I use this one and it does its job well