Why kill animals? It's not like menstrual products don't work. just keep buying the stuff that works more than others if the little difference between the testing fluids and blood are really existent.

And it's not like the products would be better with blood testing. That's not how capitalism works. It needs to work good enough to be bought with the biggest profit margin possible. So using blood for testing just creates suffering for animals for no reason other than you can put "tested with animal blood" on the box. I wouldn't see that as a plus