This WordPress plugin certainly didn't live up to its name in my opinion. The introduction suggested that this importer could import any csv into WordPress but from what I could make out , anything differing much from a WordPress export file would not be readable.
The lack of any documentation that I could find on how this importer was supposed to work made trying to use it extremely difficult. It wasn't obvious until after I had uploaded the first CSV that it wasn't going to be able to import as it was missing half the fields the imorter required (even though those fields obviously would all have the same value for each row as they were not present in the source data. You'd think that an "ultimate" importer would be able to deal with assigning fixed values to common fields - as it was the only field it catered for like that was the one where you can indicate that all the rows are 'published'. I had to go back to my original CSV and add in several extra columns.
Next, there was no option to indicate whether the top row in the CSV contained headings or not - the importer provided an option for identifying which row contained what for when there are not headings but then proceeds to not import the first row regardless of whether it is headings or data.
The final issue that I had is that in none of the dozen or so attempts I made to import the data did the actual content of the posts actually import. I got the post titles and dates and categories (once I had updated the fields in the CSV to include the category names - another thing the 'ultimate' importer couldn't do for me) but not the content of the actual posts. I eventually gave up and spent several hours opening each post and manually inserting its content.
The end result after many hours work was that I got most (but not all) of the posts loaded with their original creation dates and times (I had to reformat the date/time field in the original CSV as well before it would load). Fortunately I am not all that worried about half a dozen or so of the posts not loading as they were from some years ago and not all that significant now.
Given the amount of manual updates to the CSV that I needed to do to get this plugin to upload anything at all and the amount of trial and error involved to get it to at least load some of the fields, I think trying to use this particular importer was a wrong choice. While I would have needed to reformat all the data to get it to load via a WordPress post import/export plugin, I had to reformat just about all the CSV data to get any of it to import anyway and at least with the other importers there is a clearly defined format for the data that I would have known to convert it to. I suspect that had I spent the time to reformat the data so a less than 'ultimate' CSV importer could read it would have got my posts loaded far more quickly than the way I ended up doing it.
I definitely do NOT recommend you wasting time with this particular plugin.