So, I have been hesitant on whether to tell my case here or not:
I had bought a MiG Flash back in the v1 days and it had arrived veeery late, in a v2 form. I had ordered this in order to test how low-level it was. When it arrived and after some tests ( nothing that thorough as what
@TotalJustice has done ) I thought it was a very low level thing and it may work with the then future Switch 2. I actually didn't need MiG since most of my Switch consoles are modchipped ( long story, I don't do this professionally but I like modding things, microsoldering, and so on, and I was quite sick during some months in the pandemic and modding consoles for friends/relatives and myself was a good evasion/escape/entertainment ).
Then, I wasn't going to get a Switch 2 in this launch window, I didn't and I don't think the catalogue justifies it by now and it seems for a good while... but then I found a place in Spain which had stock and it was even lower price than MSRP and some FOMO ( hack/jailbreak/mod type of FOMO ) kicked in so I bought it.
Having seen all the discussions on MiG Flash and having myself speculated about it ( the real cart speed vs Switch 1 cart reader slot speed vs MiG Flash speed, using a faster microSD... ) I ordered a MKW bundled one and also ordered the fastest regular microSD I found ( Lexar Silver Plus 256GB, read speeds up to 205MB/s, sustained 180-190MB/s reportedly ) in order to try that in the MiG Flash. For the Switch 2 itself I got the SanDisk microSD Express card, also 256GB.
The Switch 2 and the both microSDs arrived June 10th and I tried everything was working fine. Then I updated to 20.1.1 and activated the microSD thing. I entered an account I had since the Wii U days ( very very old, never used in Switch 1 and almost unused in Wii U too, I had some virtual console purchases there but those are no longer usable on Switch ), registered my PayPal there and purchased a few things and downloaded them.
I then decided I would try the MiG Flash with a dumped copy of Zelda TotK. For that I updated the MiG Flash to the then latest 1.19 and used the MiG Dumper ( the red box ) to make a copy of my original Zelda TotK.
Now, before trying the MiG Flash with the Zelda TotK files, I inserted the original Zelda TotK cart in the Switch 2 and I paid the upgrade for 10€ ( I would later purchase a year of Nintendo Switch Online suscription to get the GameCube classic goodies and that would have given me both Zelda BotW and TotK upgrades for free, but anyway ) and downloaded it. I started Zelda TotK with the original cart and played for a few minutes.
Then, I removed the original Zelda TotK cart and inserted the MiG Flash with Zelda TotK files. I saw it did read but then I reproduced what all fellow MiG Flash users were having, read error when trying to run the game.
Speculation here in GBATemp was going on and I just spent some days playing the wonderful MKW and a bit of TotK, GameCube and some few others ( just minutes in total, not even an hour, so mostly MKW ).
On Sunday 15th I saw MiG team had delivered the 1.20 update and I updated my MiG Flash cart ( powering it in the MiG dumper, in the red box, not in the Switch 2 nor any Switch; the update went just fine ). And then tried it:
Again, notice that before using the MiG Flash I inserted the original Zelda TotK cart, extracted it and inserted the MiG Flash cart with Zelda TotK files. I ran the game again and I saw it was working fine for the first time, I took a small video, extracted the MiG Flash cart and I stored it for never using it again until now. I have used several original carts and downloaded their updates and so on, just regular Switch 2 use, still mostly MKW.
I have been using WiFi and airplane mode, both, downloading some more small games and using airplane mode otherwise, but I even had WiFi connectivity for good periods of time.
So far so good, no ban.
My take on all this, added to the few recommendations of using your own original cart dumps and now staying away from all things MiG altogether ( mostly so after the latest
@TotalJustice findings, which clearly show MiG Flash firmware has big flaws still, hopefully to be addressed in the - near ? - future )
is that having used the actual original carts of the games later tested with MiG Flash has saved our asses. My pseudo-educated guess here is the heuristics applied by nintendo ( in both, failing 1.19 and later, "working" 1.20 MiG Flash firmware stages ) may have accounted for something like "if there is a proper loading of game ID X and then/also a failing loading of the same game ID X, don't treat that as a counterfeit cart use", something like "it may be a dirty/failing cart but still original".
Anyway, what do you guys think ?