The harrower is a dogfight frame missile with an outsized head designed to carry a large charge of chemical high explosive. This makes it a lot simpler and cheaper than a seeker, but doesn't do as much damage. Even super-compressed nitrofullerene explosives don't pack the same energy per Kilogram as a microfusion warhead.
The original harrower design has been around for years, as it was designed for the navy as a cheap replacement for the seeker. The navy chose to keep using seekers, but the harrower became popular as it was so simple to make and didn't require specialist tools, so its design could be pirated and copied. 'Harrowers' on the market are usually illegal grey-market copies.
"Officers are warned to watch for machine shops being used to produce illegal
'harrower style' ordnance"
- Police report