I think you mean, what is the best AQUAMIST kit in general for failsafe protection? Both have the same failsafe capabilities but the HFS-5 kit uses a high speed valve (similar to a fuel injector by design) instead of the on/off valve system which the HFS-1 kit uses. The HFS-5 kit is far more controlled for more reliable and consistent results. Both kits are awesome and you'll see gains with each, plus the same level of safety. Search the forums and you'll find other failsafe options you can incorporate into each kit
Also, since the HFS-5 uses the injector duty cycle to keep the "alky-to-pump gas" ratio the same throughout the powerband, it uses less meth during a run.
