I'm on my 3rd PNW style external post, tons of people make them and they all work the same way. They work great but are a huge PITA to rebuild when something goes wrong. They are basically the same post as their internal droppers but use a nylon string that runs from the bottom of the post that actuates the dropper up to the top where the cable attaches. The problem is the tolerances are so tight that dealing with the nylon cable when you have to rebuild the post is nearly impossible. I'm sure people can do it but that is why I'm on number 3. I try and try until I get pissed and go online and get lucky and see some site usually jenson dumping old stock for so cheap I just buy another one. When this one dies I'm drilling the frame. I never had an issue with my old KS eten external dropper but it is ugly compared to the PNW style.
Oh and my frame is setup for external droppers so it has the cable attachments for it but I'll just deal with zip ties when I drill the frame.