The feedline should probably be longer than the radials so the rig can be setup just outside the radial circle. I have used lengths from 18 feet to 30 feet. Feedline length is not at all critical. The bandwidth is wonderful, the SWR on all bands tested is quite good. It should be possible to tune this by just measuring the length of the whip extended and get close enough to use without a tuner, even for the 20 meter version.
Field testing so far indicates it works very well.
The 20 meter version only uses a small loading coil and is about 13 feet tall and loaded well above center. It is one of the few cases where retuning is worthwhile going from CW to SSB portions of the band. But even here, the difference in bandwidth vs. a standard Hustler mobile whip setup for 20 meters is remarkable. The entire thing is light and sets up very fast, except for the fiddly bit with the radials. It takes down quite fast as well.