This is not for me as such, just I am interested in learning. My friend mentioned this morning that she was thinking of trying Vienna reins on her horse for lunging instead of the Pessoa she normally uses, because she's seen them used by our old YO (personally not a recommendation I would be swung by

).
Anyway, they aren't a piece of kit I am familiar with, have done a quick google and they seem to me to be a bit of a cross between side reins, but sliding and draw reins but fixed to the roller, not the hand???
Is that kind of correct?? Do they have merit, they seem to be mentioned on a couple of classical sites, are they preferable to side reins or as she uses now a Pessoa?
What are people's thoughts?
Her boy is quite short coupled, big (17hh) warmblood and can get quite up and tight in his back.
Personally nowadays I like using the Pessoa just fixed on the back end and not the front (yes I could just use a bandage, but have got the Pessoa and its on the roller, so its easier to bung that on) and double long lines through the roller rings to the bit, but then Minnie is more of a long and low type so doesn't need anything to encourage that.
This is really just for my interest and not advice as such as I'm not intending on using them myself. I just haven't seen them in use before, so was interested in their benefits or otherwise.