This video shows the Terrain Tamer seal cut open to better illustrate how it works (the first part of the video is about installing larger hub studs).
Start watching at 3:50 for discussion about the new seal design.
That was one concern I had also, can they handle the speed (internal friction?), but if it's a proven concept then maybe not a factor.
It would be interesting to learn what company makes them for Terrain Tamer and where. If SKF, NOK, etc, that should alleviate any concerns.
Update: apparently...
Was watching some You tubby videos out of Australia and came across one discussing the Terrain Tamer HD hub seals. Apparently the seal rotates on itself instead of on the spindle with the idea to reduce wear which is particularly important on the rear spindles which are not replaceable. The...