is it really £500+ good? Does it really outperform similar £200~ budget routers?
Easily, and then some. The usability of it, the code quality and the vast range of functions. It's the wrong thing to compare it to £200 devices. It's a much cheaper and easier-to-use Cisco. It's a very serious business-grade device that has the ease of use that puts it into a class of its own.
Ask yourself, can you read, on approx one screenful, the entire config of your router, scan it for mistakes, and difference it to see what you changed? I can look at the config examples that CrazyTeeka pointed at earlier and copy-paste parts of them. The XML config is just sanity finally arrived. (And it's optional, if you don't speak XML, then you can simply use the web UI forms same as you would eith a home user router.)
I can't imagine ever going back to a SOHO-class router. It would be far too horrible. :-)
As for code quality, the Firebrick guys really know what they are doing, and bugs get fixed fast. The big difference compared to VastCorp's devices is that you can simply talk to the authors, they have names and are on irc and email and they will listen, no corporate paralysis.
Not six stars, but seven. Take a look at the XML config examples, the wiki and the manuals.
