Anyone installed one? Did you need a lenght of brake housing, like in the SRAM videos, or can you get away without it by using string/gear cable/etc?

Depends how big your hole is (if you pardon the expression). If your routing is tight then a length of hose is useful, you’ll get the red coupling bit in the packaging with the new post. I don’t think it will screw in to gear housing and I wouldn’t be using string. You only need the spare bit of hose to be long enough to go through the frame from the hose exit point out the top of the seat tube. With some frames this is only 30 cm or so.

The YouTube videos are pretty handy for bleeding as well, by the way

The red coupler screwed into some gear cable for me, no problem, and worked with (almost) no hassle – lesson 1 – put the rubber grommet in first, THEN the cable.