RF, that will work, but voltage control will be a bit sloppy, as it does not reflect the losses in the secondary under loads.
Using the little tranny gives exceptionally stable voltage control..... better than most of the commercial ones, and load recovery is simply amazing. If you switch in a few kilowatts, there is no light flicker or dimming..... and from 0 - 5kw, the output voltage does not sag.
............oztules