not only will it hurt performance but you will be running the fuel maps for low rpm while the valves are opening for high rpms, timing will be off, and basically with long term use the engine life is decreased. also the vtec piggyback controllers do the same thing, so unless you get a controller that will also adjust your fuel map the controller will do the same as the toggle. get your ecu socketed and a rom editor or get it chipped, anything else is just bad engineering.