This certainly looks easy to make and is inexpensive, but is it safe for your computers? Anyone here ever tried it?
I think that serial cable won't help you at all (unless you own an old computer with Rs232 serial port).
The most economic solution is to get something with USB interface, like the ones in this list:
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20201022061700&SearchText=usb+serial+ftdi
Like this one:
https://www.aliexpress.com/item/4000479540191.html?spm=a2g0o.productlist.0.0.68fc324a2AayPC&algo_pvid=e75223a6-b955-48d1-926d-82c7aa771fec&algo_e