I agree with both gents. Asking for your QR code seems rather random at immigrations. Sometimes they do, sometimes they don't. I have the idea they simply check their system when they do. Filling out a TDAC takes a few minutes, no hassle at all. At least for me, not worth downloading another app and again sharing passport details on the online highway 

I have never been asked for the TDAC but the guy next to me did not do it.  When he tried to go thru, he was sent back to fill it out.  I assume it should be linked in the system to your passport since it requires your passport number.  When they scan your passport they see that you filled it out

Just landed and am in my taxi to Soi 11.
I never installed the app. I just did my TDAC as usual. And as usual they never asked to see it anyway. THIM definitely not mandatory yet, but I still don’t know about TRIM, haha

Thanks everyone for the information as I'd not heard of this. Have installed the app, registered, scanned my passport and done the facial recognition so all I need to do now is add my trip 72 hours before to get the QR code.

Sorry one point of clarification. You do your arrival card within the app, but the app I also does other immigration services and not just the TDAC. For a regular visitor it’s worth using the app just so you can save your passport details in your profile making it easier to fill out your arrival card.