For like the ZEX kit, the Nitrous is engaged when your at WOT, so all you have to do is arm it. For the other brands like NX and NOS do you have to arm it then push a button to engage the Nitrous?

 

For the NOS and NX and every other kit, you also have to arm it first and then be at WOT too. Well if you can mount the arming switch right around the shifter so you can trigger it with your thumb, I guess you can get by without the RPM switch. Arming switch is only desired if you want to be using the nitrous in 1st gear and up. But if you are a highway racer and will only use nitrous in 3rd gear and above, I think you can get by without one.