I would recommend NEVER buying anything from "Hans" or his handful of other shady businesses (he frequently shuts down old online businesses as they gain bad reputations and opens new ones, in an endless cycle of BS). These are all owned by Pete Rothenbacher of North Carolina who is a known crook. His game is reselling junk quality parts from unknown knockoff manufacturers, bought by unfortunate folks who have forgotten (but will sadly soon be reminded) that "low price" and "good value" are not always exactly the same thing. Those parts of his are responsible for thousands of destroyed VW diesel engines, mostly TDI engines. Timing belts that shred after a few hundred miles.... injection pumps that seize and throw the timing belt.... etc.
Read about folks' experiences with his parts on tdiclub.com and get a feel for what this guy's sense of ethics is. Nobody has ever been able to get him to help with the massive costs of repairing the damage done by his parts, at least to my knowledge. Those folks who bought his con discover that the few dozen dollars they saved on the cheap parts need to be repaid orders of magnitude greater to get their ruined car back on the road.
Even if you did happen to identify a low-risk part (which to me would not include pistons or any other internal or moving component or any part of the fuel system) to buy from him that you thought you could experiment with safely, I would still recommend against it, simply on principle of not supporting his enterprise.
The difference between the two parts you asked about?
- Kolbenschmidt pistons are known to be excellent quality based on decades of market experience. Kolbenschmidt is an above-board parts manufacturer with quality control policies, a distribution network, a warranty department, and relationships with vehicle OEMs. They are sold by retailers who are sufficiently confident in the product to disclose who manufactured it -- in fact they are proud to do so.
- "Hans" pistons are.....?????? All you can know for certain about them is that they are being sold by a guy with a well-earned reputation for selling dangerous junk that he will not stand behind after it destroys your asset. You know nothing else. No brand. No assurances about quality metallurgy. No info about where and by whom they were produced. No info on warranty performance, other than Rothenbacher's own claims which are unverifiable. Nothing.
You can probably guess my personal view of this choice. I know Tom Bryant has gotten lucky with some parts from Hans and I have seen him recommend them before. I always thoroughly respect Tom's opinions and I know he doesn't reach them without a lot of careful consideration and data. But in this particular case, I strongly disagree with his perspective, and point out that his positive view is ONE opinion, pretty much the only verifiable positive opinion of Rothenbacher's parts you will find. I refer to you to the hundreds of tragic stories referenced above as the counterpoint to Tom's solitary, small-sample-size positive view.
Mahle pistons are also excellent quality, similar to KS.