Personal opinions:
The S1 is a tricky turbo to tune, and there are several reports of failures even on turbos that had sensors and were never overspun, some of them being blown seals and others catastrophic. Wastegate duty is not a good indicator of headroom on small turbos in general, but on these it's especially misleading, so many of these will have the wheels blown out of them.
Between what appears to be a low tolerance for overboost, the inherent quirks of boost control on these units, and customer expectations not matching the hardware, we're going to see a lot of these fail. It's a perfect storm. People see the Garrett name and their pie in the sky ratings and think it's more than an "IS38+", and it's really not. They're clearly selling well because i'm getting at least 1/week for custom tuning, and i can tell by some of the setups and customer interactions that some people do not understand the limitations of what they purchased. We've only had a couple on the dyno, so take it with a grain of salt, but so far it looks like they make about 30whp more than an IS38 if Garrett's shaft speed limits are respected.
I have 3 or 4 active now, and in total EQT has probably tuned a dozen of them. To my knowledge we've had no problems at all, but Ed took a very scientific approach to the first few and that has given us a lot of good data to implement in all of our custom tunes.
Ultimately they are responsive, spool well, and offer a nice little bump in power over an IS38, but if the expectation is to punch in the same weight class as a lot of the hybrids, the customer is going to be disappointed. If the shaft speed limits aren't adhered to, the wheels are not going to stay on the inside for long.
