Lets get somethng straight here - a penis pump is not going to give you a massive member akin to the great John Holmes overnight, within a week or so of frantic pumping the outcome would probably be a very sore penis & a bicep to outshine popeye!
A penis pump will help you maintain a bigger, stronger erection just before sex & an increased length & girth over time with regular sensible use.
A pump can also be a great masturbation tool by simulating the sucking effect of oral sex on the penis.
Happy pumping!