This is Sony branded DDS-4 compatible 4 mm data cartridge, model number DGD150P.  It has a native capacity of 20.0 GB and is 150 m long. It's still sealed in its original packaging, but it's been sitting in a cupboard for years.

I'm not sure how combined postage will work with Simple Delivery, so if you're buying multiple items and eBay wants an excessive amount for postage, please get in touch before you complete check-out.