IF this is a new record, the category field will always be empty, so I don't see the need for an If step here.
In any case, you might set a field option on category to auto-enter "Other" each time a new record is created. No script is then needed for this. You can just type in Other in the Data box as the Data to be auto-entered in each new record.
(And I suggest using Set Field [Table::Record_Category ; "Other" ] instead of Insert Text for cases where you want to use a script for this. The "insert" script steps require that the target field be present on the current layout. Set Field does not, so this makes it a bit more reliable than Insert.
I feel stupid that I didn't realise that.
Thanks for your help.