They’re not just for imaging. The 1.25” version can be used on 1.25” only system such as TV-60. I am yet to see a difference between a Tele Vue 8mm Plossl with 5x Powermate and Vixen HR 1.6mm using a TV-60 when viewing Venus. (Further tests yet to be done).
See
https://www.televue.com/engine/TV3b_...d=53&Tab=_back
and
https://www.televue.com/engine/TV3b_...id=53&Tab=_app
Visually they are superior to Barlow’s in they do not alter the exit pupil and the way the eyepiece sees the incoming rays.