IIRC, Phorm required a cookie being set before it would switch off. That, in itself, was an issue, given that the only way your browser would send that coookie was if it thought you were requesting something from the relevant domain. So, with Phorm, what we actually had was a bunch of boxes sitting in the ISP, injecting fake redirects in to all requests and passing them through a seperate domain, checking the cookies, and then allowing traffic to pass unmonitored if the right cookie existed. You could never be certain that your traffic was not being monitored. It also meant that you had to "opt out" of phorm with every device on your network.
With this system, what you have is a web browser set to use a proxy server. Switch off the proxy setting, none of your traffic goes to the proxy server. No fake redirects, no promises to not look at your data, no effect on other machines attached to your network, just a complete lack of connection to those proxy servers in the first place.
So the two are actually quite different.