Small offline tools.
A client trusted you with these files. You are the virtual assistant, the nonprofit ops person, the one-seat bookkeeper. Someone is waiting on a sheet back. You cannot put this client's CSV on someone else's computer.
Put warehouse stock on every catalog product — blank stock stays, leftovers that were never listed go — and both files stay on this computer. Nothing is uploaded.
Lite cannot do that. Lite is free: two files, stack, dedupe, export. Kitchen does this job — $19 one-time, Polar emails a zip. You get the sheet back without uploading.
Tools
Kitchen is the $19 zip Polar emails. Lite stays free for stack and dedupe only.