I have a GTI DSG and had the APR Stage 1 91 High ECU tune for about 3 weeks without the TCU. I read mixed reviews so I held out. I would basically say it can work without it but isn't truly up to the task.
In my experience, when in 'D' and upshifting during normal city dirving, momentum would drop abruptly between gears and it mostly upshifted to below 2000 RPM. Immediately after the APR TCU tune I noticed 'D' mode shifts were smooth and shift points consistently stayed above 2k in moderate to heavy acceleration. And the biggest improvement after the TCU tune was how it responds now to throttle input - it stays in the same lower gear for an extended time when giving it juice, whereas before it would force an upshift WHILE getting on it (that probably annoyed me the most, felt like I surrendered all the new power over to the stock DSG MasterLord, haha).
Yes. I wouldn't say I bought into that statement at first, but hey, it happened to me.
I have exactly the same sentiment for the GTI. The matched shift points alone makes it a winner.
On a related note, and a rant of mine, the modern pre-ignition phenomena in DI turbocharged cars, LSPI, is worth putting on your tuning safety checklist. When an ECU tune unleashes power for a time in the LSPI zone (technically 1500-2000 RPM; most dangerous in high gears at highway speeds) it becomes all the more important to watch shift points and lugging, far more than the average "good" driver does. The sense of having plenty of power in low RPMs is a false sense of security. I found overall that the APR TCU tune matches the additional power quite well and is much better at adjusting to road inclines. You might consider a TCU tune as protecting your investment.
Happy motoring!!