I had never even heard of Eko! After seeing its pictures last week I immediately felt a strong click (after having been on the lookout for a proper bass for two and a half years -- all other instruments were too much a 'guitar' and did not feel much of a 'Bass'). I traveled half the country last Saturday and purchased it from its previous owner.
It is an original Eko instrument 'Basso Acoustico Quattro' built in May 1980 in Italy. It is really huge, has a good deep warm sound, a solid wood top, a wider and fatter neck than usual (upright bass dimensions except for the flatter fingerboard and 34" mensure), is fretless, and has a floating bridge. No pickups/electronics whatsoever. Pure, honest wood and strings. All of this exactly what I wanted but so far never found in other basses.
Now in the process of testing my favorite strings on it, perhaps improving nut, bridge, and neck setting, making the tone even more double bass-like through subtly damping the decay, sustain and higher overtones.
Although technically it is a bass guitar, it is rather substantial (huge!) and I intend to play it upright and use double bass technique, instead of bass guitar technique, as much as it will allow.
I'm super happy!
Cheers and happy fundamentals,