I don't know what "liss" is, but Kerapremium is the original Max formula, and that's what I started with. If your hair is fine, the curl relaxation will likely be permanent, at least to some degree.
None of the BKT formulas has left me with straight hair. My initial application was a total disappointment--there was almost no curl relaxation. I was still a strong 3c after the first app, so I did it again immediately, and the curl relaxed to about a 3b. Still not satisfied, I waited 2 weeks and did it again, resulting in 2c/3a curls. Satisfied, I waited a month, then the curl seemed to be returning, so I did another full-head application, and the resulting curl pattern was about a 2a/b--almost too straight.
It's really hard to know exactly how your hair will react. There are many contributing factors, but the primary determinants seem to be hair texture (fine vs. coarse) and curl tightness.
The only thing I can say with any certainty is that I love my hair. I have struggled with my hair my entire life. I don't wear my hair straight, but if I want it straight, it takes almost no effort anymore.