It's worth buying if you want or need a finishing/polishing stone. There are less expensive synthetic stones that will do the same job, for example, the Shapton Pro 8000 or 12000.
People's Hone of Indetermite Grit. A tongue-in-cheek name for an inexpensive Chinese sourced stone of somewhere around 12k that is popular with straight razor aficionados.
we use to call then CHIGs, CHUGs etc.