The problem with the Tein S-Tech is not the quality, but the spec. The spring is too short, particularly in the rear. The piston is too low in the stroke when static. We all know that factory dampers don't like to go too low. This has little to do with manufacturer. General rule of thumb has always been to swap out OE dampers if you plan on going low. Nothing new here.
The S-Tech is actually a more aggressive, more handling biased spring than the H-Tech. The H-Tech was developed for drivers who wanted to go a little lower without sacrificing too much in terms of ride quality. Hence the longer rear spring and softer rear rate.
Tein makes a great spring. They are progressive rate, and use high quality spring steel. If you want to use a more aggressive spring, be it the S-Tech or similar, then you need to use appropriate shocks.
Paul, my vote is for the Ohlins springs. I would assume that they are matched to those shocks, so it would be hard to do better, especially when we are talking about Ohlins. They seem to know what they are doing.