The Nazir is the second known multi-static radar system in the world of this kind. It is not an OTH-B radar, the Iranian OTH radar in operation is still unknown.
The closest system to it is the Russian Struna-1, but the Nariz Bina combi have a much larger range.
It is kind of a path to a solution for Irans biggest problem and advantage: Mountainous terrain.
OTH-B is one solution, a multi-static network radar another solution.
The Nazir is in so far unique that it is kind of the first "hardened" radar. The circle pattern emitter site can take the punch of enemy weapons and still remain operational or partially so. Almost no other radar offers this and it is a important improvement for a large early warning radar.
The Kayhan radar does the same job, is mobile but lower ranged.
Its low level and anti-stealth capabilities are its most important ones. Each Nazir node could cover a circle of 300-600km. With a dozen Nazir and Binas most of Iranian terrain could be covered.
Honestly speaking, I thought the Keyhan is the mysterious OTH-B operating in Iran. It is not the Ghadir and the Sepehr should be a future ballistic missile early warning radar, not a OTH-B.