I found this command line utility that doesn't show the GUI output but gave me what I needed: https://github.com/na-ka-na/ExcelCompare
Sample output (taken from the project's readme file):
> excel_cmp xxx.xlsx yyy.xlsx
DIFF Cell at Sheet1!A1 => 'a' v/s 'aa'
EXTRA Cell in WB1 Sheet1!B1 => 'cc'
DIFF Cell at Sheet1!D4 => '4.0' v/s '14.0'
EXTRA Cell in WB2 Sheet1!J10 => 'j'
EXTRA Cell in WB1 Sheet1!K11 => 'k'
EXTRA Cell in WB1 Sheet2!A1 => 'abc'
EXTRA Cell in WB2 Sheet3!A1 => 'haha'
----------------- DIFF -------------------
Sheets: [Sheet1]
Rows: [1, 4]
Cols: [A, D]
----------------- EXTRA WB1 -------------------
Sheets: [Sheet1, Sheet2]
Rows: [1, 11]
Cols: [B, K, A]
----------------- EXTRA WB2 -------------------
Sheets: [Sheet1, Sheet3]
Rows: [10, 1]
Cols: [J, A]
-----------------------------------------
Excel files xxx.xlsx and yyy.xlsx differ