Hi,
here it is my question:
Exception made of its (very bad) hability of being decoded,what are the advantages of this testing version ?

I read:
no internal clippings anymore
canonical huffman codes
time resolution of the psychomodel is now three times higher
If I understand,this version is higher quality than the older one...

maybe it avoids even more pre-echo...

Well, it's a "test" version and should only be used for "test" reasons. That said 1.95z6 is a testcase for the upcoming SV8 so those improvements will probably be part of the official SV8 encoder. You can use it as you want but the problem is that the fileformat could change from day to day breaking compatibility with your previously encoded files (those encoded with 1.95z6 that is).