So it doesn't just cache apt downloads but also wget and curl downloads too.

I was going to ask the same question and found this thread ..

We use apt-cacher-ng , and it does a great job at caching debs. 

I set up apt on tkdev to use our cache:

echo 'Acquire::http::Proxy "http://apt-cacher.fantinibakery.com:3142";' > /etc/apt/apt.conf.d/01proxy

that works for all other deb systems.  But not tkdev  .  Looking further each product has its own /var/cache/apt/archives .   Probably a change root thing used during make. 

This is not an urgent issue , I know there are a lot of other things being worked on .

To make the builds use aptcacher-ng you would need to install it into them from the start and then you would need to add the config. If you wanted to end up with vanilla appliances, then you'd also need to remove the package and the config after the build. If it is for your own use and you want them pre-configured to use your apt-cache then you could just leave it.

The initial setup shouldn't be too hard (add apt-cacher to one of the base plans and make the conf an overlay and add it to the base makefile). But TBH I'm not sure exactly how to remove it all again...

TBH I'm assuming that is why TKLDev uses Polipo instead (much easier setup).