Originally Posted by jagatron
The travel agent coupled with the 8 speed is a friction installation...
If you're talking about the one that was linked, the picture caption says it's indexed, and the creator further specified it as such in some of the posts he made on various sites.
There seems to be a debate about whether indexed shifters for derailleurs have linear pull across their full range of travel. The creator of the Travel Agent + bar end shifter has stated while the hub seems to work fine being shifted like this, he does not know if all eight gears are really lining up correctly inside the Shimano 8 speed hub or what the long term durability will be.
This Jtek bar con is said to be engineered specifically for shifting the Nexus 8/Alfine hub, with cable pull that matches Shimano's shifters for these hubs.