The thinking is that DSG tunes do a few things…
1 raise red line - not really necessary on a 09-12 s4 DSG as it reclines at 7000 (vs tcu 7200) but 200 rpm on an engine that can handle it with a blower that can handle it will help (not sure if this applies to the B8, just generally speaking). The13+ cars with DSG have a 6200 rpm red line so the pickup is actually substantial going to 7k+, and is worthwhile.
2 increase shift speed - we know that’s not going to do much vs stock DSG which is insanely fast
3 add lunch control where it doesn’t exist or adjust existing launch control - here again we have seen that this doesn’t really help much. The fastest guys don’t use launch control I don’t think… And even then they’re (fastest with/without) pretty much equal. Launch control on a DSG car works reasonably well already and launching without it is pretty straight forward so this isn’t a huge beit. 2010 cars don’t have launch control so it’s a nice party trick for them, but as mentioned, the fastest launch times have been done equally by LC and non LC cars
4 change patterns and characteristics of the transmission’s 3 modes (D, S, Manual) - not sure if the existing tcu tunes do this or not
All in all it sounds like the 09-12 DSG guys don’t need a transmission tune…but the 13+ guys do.
If buying a 13+ DSG that means today GIAC is the only game. Tomorrow could be GIAC, APR or revo as the others are working on one. Primetime may already have the APR tcu beta on his car so sounds like they’re close. His poker face is terrible.