Do I have to use the pricy o2 sensor in my 99?

I got a new exhaust and need a new downstream o2 sensor. Do I have to buy the one that is "supposed" to be for a 99 downstream 4 wire one, which costs like $75 or would a less expensive one work? It is my understanding the downstream sensor is simply an emissions thing and doesn't affect the tune of the engine, is this correct?

NTK or Bosch from RockAuto. $39 plus shipping, Google a discount code to knock a couple bucks off.

Sweet thanks!