Is Opera Mobile worth buying?

Opera Mobile is quite a different thing - Opera Mini uses a proxy server to analyse the page and just send you a stripped-down version, and there's very little rendering going on on the phone itself. Opera Mobile is more like S60 Web - it downloads the whole page and renders it on-device.

I don't think Opera Mobile is that popular, but you can download it to try free, and see if you like it:
http://www.opera.com/products/mobile/products/

Opera Mobile lets you download torrent files that you can use in a app called SymTorrent and many other foreign formats that the default web browser in your mobile phone would otherwise reject. A good example of this would be an .avi video extension file which you've downloaded for playback in say CorePlayer, since there is many combinations of media the N95 can play natively it's a good ''second browser'' to have.

I didn't know about this rendering thing. That explains why I've been finding mini so quick.

Knowing that I'd not upgrade as I only want it for surfing and I've been really impressed with how quick sites load compared the the native app. Facebook for example is now really usable, loads in a couple of seconds. Excellent.

Trouble with Mini as I recall (from some time ago) was that it asks which connection you want to use, every time you load a page.
I also seem to recall that Mini doesn't allow you to configure keypad shortcuts very much - and specifically, forces the use of asterisk or hash WITH a key ... whereas Mobile allows one-key shortcutting - it's this that makes Mobile a winner for me.

for mobile browsing realistically mini is fine. It's only if you cant wait to get to a pc and you need to download 'unknown' file formats you'd need something other than the built in browser of mini.
As said above, torrents files could be a good example of a file needed to be downloaded but really Id rather wait till I can get to a computer than use a cellphone.