I've dabbled with Fasterfox and couldn't find any noticable performance improvements.
In addition to that, I don't really 'trust' the features it implements. Link prefetching doesn't fit into my usual web browsing workflow and it just uses up bandwidth unnecessarily. A lot of the network tweaks may be advantageous to the end user, but are rather unethical when you look at them from a web developer's perspective – bombarding servers with simultaneous connections and pipelining, I believe, is a source of much aggravation. These network tweaks can be implemented by editing some variables in about:config, anyway, so there is no real need for Fasterfox in that sense.
The Tweak Network Settings extension is largely similar in that it just utilises the existing configuration capabilities in Firefox and acts as a front-end. Even then it's not a whole lot of use – if you don't understand the terminology browsing through about:config, you're not going to understand it when its thrown at you in a seperate window!