Kris is using the steel braided Magura brake line. The pic on unicycle.com shows the stock plastic brake line. The braided brake line is much more flexible than the plastic line and that is probably why Kris has less slack.
One problem with a brake line is the line getting snagged when you try to catch the muni after a UPD. Having less slack makes it less likely that you will snag the line and break it off.
Less slack is better, but there is a limit to how little slack you can have with the unflexible plastic line.
There is no need for the braided line, however, if you make the hose long enough to take the seat off, then spin the seatpost around several times before tightening.
In this picture, I left the hose the length it was on my bike, so I could switch between the two. It’s all grabbed tight and taped to the frame. It still workes, but the line was warped after that (fine for uni, fine-but very ugly for bike)