Fantastic! Simple and straightforward. And unobtrusive, to boot. The easiest and quickest way to add proxies and rotate among them.
Only one suggestion for improvement: please make the Current Proxy field blank if none of the proxies currently at work. Once one turns a proxy off, the field should become empty, without showing the top one on the list. There's always a risk of accidentally removing a valuable proxy if it happens to be this top one.
Otherwise, just excellent! (Sometimes it seems the proxy lingers for some time after turning it off. Very weird feeling, though.)

for pentest must use this :)