Ok, so running it takes longer than expected, and this was only the zero-out data, not even the 7 or 35 passes.
I am not sure on the results... following the process, I would say data is erased, but when I look at the restore results from MacKeeper, some data seems to be left. The oddity is though, that these results are nothing I have ever deleted (it only comes up with .plist, .tiff, .xmls and .jpegs with filesizes somewhere between a few bytes and approx 2Kb). Files that used to come up in these results (MP3 files, for instance) are nowhere to be found anymore.
Are these small files false hits or something, caused by the zeroing out? (See screenshot)