As a long-term user of Quad ESL 57's, I can't think of a Speaker that can be purchased for such small monies and is able to create such a good impression when compared to later Quad ESL Models and a broad range of Panel and Cabinet Design Speakers.
Where it is a sticking point is the ESL 57's age, with the Youngest Model is able to be found being approx' 30 years of age.
Between 30 - nr 70 years, is the age Speakers are to be found today.
If the OP or any Interested person was keen to try a ESL 57 or ESL 63, if they were able to discover a very reliable support service within a few hours from their home, I would happily encourage the punt on the Speaker, I would not even suggest a audition was to occur in advance, as their is great value to had for the cost associated.
Without a readily at hand support, age related issues developed or yet to manifest will spoil the experience.
I have bought beaten up pairs for £100, passed them to a friend and a few hours and an extra £50 has got them functioning to a point they have been used in a Public Exhibition.
The Link shows images, of which the 57's rotated 90 degrees are said speakers donated for this cause, to introduce the audio public to such a concept for the 57's. Other exhibitors were offering the conventional usage of the 57.
http://www.adventuresinhifiaudio.com/19/03/2019/the-wam-hifi-show-march-1617-2019-kegworth-hotel-packington-hill-kegworth/