lack of fuel control and inability to properly atomize the fuel and nitrous to prevent hotspotting.

only the NX kits and NOS dual nozzle kits are able to do this with their patented dual nozzle tips that atomize the nitrous along with fuel right at the nitrous injection point.

all other kits simply rely on increased fuel enrichment due to WOT, require you to run rich all the time, or retard the ignition to safely dispense anything more than a 50 shot reliably. they may shut off during a lean event, but in most cases, by the time it shuts off it's already too late.