I think $40 a year just for the split feature is a little too much. However, adding more useful features for manipulating CSV files would probably change my mind about it. For example, doing some reorder or preprocess of the files as if people split into X files they'll have to do that action X times if they do it in Excel directly.
Check out the Didgets tool at https://www.Didgets.com which will let you import data from CSV, Json, Json Lines; filter out any unwanted rows; and then export it out into CSV, Json, Json Lines, HTML, or XML files while splitting them up like this does.