So you read about an "APT caching proxy" and that it can "save time and network bandwidth."
Sounds like something you should have, right? After all, the trade-off is just some additional disk space. APT already has its own cache at /var/cache/apt/archives/, so part of what the caching proxy would store in disk is already there.
Truth is, for a single client a caching proxy might not provide any benefit and might even cause a slowdown, but for at least one of the alternatives it is even worse: every request that goes through the proxy that requires a download from a mirror creates a new connection.
It is 2012 and a piece of software that aims to "save time and network bandwidth" can't even use keep-alive connections?