why do people use air injectors as opposed to a boost controller like gizmo or greddy?

if i opted with an electronic boost controller how hard are they to fit and wire in?

what do you do with the original amal valve wireing...i.e. if you chop it will the management throw a wobbler?

and are they generally a safer way of controlling boost over air injectors or the original amal valve?

it has just occured to me as a lot of the jap boys use boost controllers whereas cossie boys use air injectors?

i am not even gonna talk about manual boost controllers as i think they are a bit of a crude way of doing things!!!!