The tab for an installed add-in does not appear in Excel's ribbon, but the add-in is checked in the Add-Ins dialog.
A Microsoft Office Update for July 2016 causes Excel to block files which were created on another computer, due to potential security concerns. The add-in will load successfully when it is installed, but when Excel is later restarted, it will not load the blocked file.
Note that this can occur for any third-party add-ins, not just Peltier Tech's.
Remember, if you receive an updated add-in workbook, you must unblock the updated workbook before it will open.
If you have not licensed the utility, go to Peltier Tech Charts for Excel for more information.