i agree with wolfie, a "second shot" on a button is potentially dangerous for the engine if activated at the wrong time.
you'd be better off using a progressive controller for a smooth delivery of N2O.
As i said , the "second shot" button will only activate at what , but then should only be activated at the correct RPM , the user MUST HAVE A BIT OF COMMON SENSE
as in the fact we trust drivers not to slam it into first gear at flat out in 3rd and dont need a box of tricks to stop the driver from doing this .
A progresive nitrous controler is definatly the way if you can afford it , but is not the ONLY safe way
but if you only take advice from people trying to sell you expensive bits of kit what do you expect ?