I think the TG splines are more comparable to a square tube shaft than a tight tolerance unit that can be balanced. At least they advertise that it isn't designed to be balanced, but I'm sure people have made the purchase thinking it was the equal of the Marlin Crawler unit.
I don't know for sure, but I suspect the Marlin kit is the same, or similar, to the long travel splines used by Jesse at High Angle.
