I met a friend at a star party last month, and he was using QHY294 color pro, and we compared my ASI183MM pro & ASI533MC pro vs the QHY294 color. The conclusion was:
1- Both companies use the same sensors from Panasonic and Sony
2- ASI has a little advantage of having auxiliary USB ports in the back of the camera which act as a free USB HUB and thus reduces the burden or cables a little

Other than that, both have the same features, and ASI for me works very well with INDI/KSTARS as well as QHY to my friend with KSTARS...
 I use the QHY Polemaster, and I was surprised by the quality of this small camera...

In general, IMO they are neck to neck in the race...

Yes the ASI120MM has issues with Linux. It is a hardware issue with the USB controller. ZWO is aware of the issue, but no firmware fix is possible.
It may be possible to compile a custom Linux kernel with a single edit to the USB Core module to handle the non-standard packet sizes normally.
That being said, I have one, and it works well enough with a Raspberry Pi4 for me with just the compatibility firmware.

True. however, it should be pointed out that the ASI120MM/MC are no longer sold by ZWO. Nor is the ASI130MM which is a very old camera. AFAIK it is a firmware issue and not a hardware issue. There is a so called compatible firmware that can be loaded into the ASI120MM/MC but then imaging is limited to 8 bit only if you manage to get it to work at all. I never did for example though success stories can be found on this forum. In short: these old cameras should be avoided because of the USB issues.

The ASI120MM/MC-S (USB3) work flawlessly (apart from the occasional driver issues which usually get solved very quickly).

Yes it is a firmware issue and not hardware issue. The so compatibility firmware just makes sure that the max packetsize follow the USB 2 specification and is 512 rather than 1024 bytes.
However, the issues are still remain. Switching to 8 Bit helps but there are also randomly issues (and it is for sure not the cable).
In 16 Bit mode it is like tossing a biased coin, towards not working.


./zwo_FWTool_USB2 -i ../../../firmware/USB2.0/ASI130MM.iic -t li2c
[36233.666737] usb 1-1.2: new high-speed USB device number 8 using ehci-pci
[36233.919714] usb 1-1.2: config 1 interface 0 altsetting 0 bulk endpoint 0x82 has invalid maxpacket 1024
[36233.921050] usb 1-1.2: New USB device found, idVendor=03c3, idProduct=130a, bcdDevice= 0.00
[36233.921054] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[36233.921056] usb 1-1.2: Product: ASI130MM
[36233.921058] usb 1-1.2: Manufacturer: ZWOptical company
[36233.921060] usb 1-1.2: SerialNumber: 00000

./zwo_FWTool_USB2 -i ../../../firmware/USB2.0/ASI130MM-compatible.iic -t li2c
[36214.974532] usb 1-1.2: new high-speed USB device number 6 using ehci-pci
[36215.188389] usb 1-1.2: New USB device found, idVendor=03c3, idProduct=130a, bcdDevice= 0.00
[36215.188393] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[36215.188395] usb 1-1.2: Product: ASI130MM
[36215.188397] usb 1-1.2: Manufacturer: ZWOptical company
[36215.188398] usb 1-1.2: SerialNumber: 00000

The binary diff between the two firmwares is:

$ cmp -l ASI130MM-compatible.iic ASI130MM.iic | awk '{printf "%08X %02X %02X\n", $1, strtonum(0$2), strtonum(0$3)}'
000001FA 02 04
000002A6 02 04
0000031A 02 04
0000038C 02 04
00000958 02 04
00000B48 02 04

One can for fun, change the "02" to "01", then the USB kernel layer complains:
config 1 interface 0 altsetting 0 bulk endpoint 0x82 has invalid maxpacket 256

Anyhow, it is still a shame, that ZWO is not able to fix the firmware. At least they could release the code and somebody would for
sure fix it for them. Just search on github.com for ASI120mm, you will find some projects reverse engineered the SDK library.

I am wondering how many INDI users had to sell (stop using) there 120/130mm cameras.
I bought a used Starlight Xpress guider and did not regret it. 130mm was my only and last ZWO product.

Interesting replies there, thanks all for sharing your experiences with Zwo - QHY products, I see that like on CloudyNight it's a toss up between the two brands. 
Some have great experience with one and bad ones with the other, and vice versa. The thing is as usual on the Internet we're always quick to complain about something broken but slow to praise something good.
 

I have been very happy with the 2nd-hand QHY183C I use with my Z61. I have encountered zero INDI/Ekos issues. The image scale would be a nice match to the Redcat, but you might be looking for a larger sensor even if it means larger pixels.

The compatibility firmware helps but it is not a true solution to the fundamental issue. Which is that the USB controller hardware sends non-standard packet sizes.
Those packets work ok on Windows because they are not handled as a security vulnerability the way the Linux kernel does.
Link rot is an issue, but I managed to dig up the old discussions I found on the issue.
bbs.astronomy-imaging-camera.com/d/6901
bbs.astronomy-imaging-camera.com/d/7132
I never managed to compile and install a custom kernel for myself. But it would be nice to know if someone can try and report back.

But the bottom line in regards to the main topic. I believe they would've fixed it if they could, so I would not hold it against them.

I did do this several years ago when I still had an ASI120MC (USB2). You need to install the kernel source package of Ubuntu, make the change to one of the C files (basically disable an error when the package size is invalid) and recompile. Then the camera worked for me. There were instructions somewhere (sorry, it's been a long time since I did this) and I am not sure if those instructions still work since the kernel source has evolved a lot since.

Just found this old thread from 2018 where I added a link to the kernel instructions but the link seems to be broken now:

indilib.org/forum/ccds-dslrs/2131-asi-12...ailes-to-expose.html

Hi all, my experience has been this. A few years ago i purchased a QHY163C. Initially everything was fine with using it with indi, but then QHY did a driver update and i was never able to get the thing to work. Even the cooling oscillated.

I rebuilt my computer(s) RPi4, tinkerboard, even my laptop, nothing helped.

After talking to QHY, their first response was does it work with Windows 10. I dont use windows so was never able to test it. It basically got to the point where i had to sell the camera because i just could not acquire or download photos.

I eventually bought a ZWO ASI 071 and have never had an issue with it using the same computer(s).

ZWO are on top of their game when it comes to drivers, but i suppose they have an interest in making sure things work under linux because they sell the ASI-AIR. QHY on the other hand, do not really seem to care about those who use anything linux.

Just my experience.

Thanks everyone for your inputs I decided to get the ZWO 183MM. Was going for the QHY model, but I will need that little hub at the back of ZWO camera.

Just advise before you commit to ASI183MM is to check your pixel resolution per arcsec astronomy.tools/calculators/ccd_suitability. The SONY 183MM/MC sensor has a very fine 2.4micron pixel size which I found it put my portable Z61 in a VERY sweet sport (and I LOVE IT) but causes oversampling with the C9.25 even with focal reducer (on which I use the larger pixel size ASI533 3.76micron and optimal seeing conditions)