I guess the way it provides the speed is buy accessing the site on Opera's server then pushing that to the phone. The downside of this is that if a site has a mobile version it will not always load the mobile version. It depends on the site. I downloaded it a bit ago but haven't played with it too much. I did try bestbuy.com and it didn't render it too well. When I tried bestbuy on Safari it loaded their mobile site.
Another down side is the zoom. It only has 1 level of zoom.
I do like the "speed dial" icons on the home page. It makes it quick to access sites you visit regularly. That's a feature of Google Chrome I use all the time on my desktop.
The Opera servers will act as a man in the middle for any transaction including TLS/SSL. The only advantage is speed which for an information consumption standpoint is an advantage. If you are also sending confidential information it it not secure and shouldn't be used.