I never seen it, in any of the well known books on accessories; the statement of the seller is correct : is neither a Micro- nor an Endo Visoflex, even if the sliding focusing glass is apparently the same as the Micro. The pics are of very good quality : I picked the 3 that for me reveal the most interesting details :
1) The standard LTM mount ; notice the 5 (suppose) screws and the scrapped metal around them : clearly a not too fine work... Leitz factory ? Uneven... The red plastic "button" glued (I think) to the Viso body hasn't an evident function (aligning to...?), but it looks identical to the well known Leitz component used in the first BM lenses (Summicrons and so).
VisoIII_LTM_1.jpg
2) The front flange : the seller doesn't detail which is its diameter/thread measure (I seem it's threaded inside, even if in the pic is not so clear) : is the most "non standard" detail : clearly, was used to fit the Viso to some optical assembly; I think it's at all custom made : the conditions are excellent (notice again the 5 screws, strangerly unevenly spaced). He who made the modification didn't take care of removing the original small button+lever assembly for fitting to the Viso devices with the standard Leitz bayonet mount: it's well visible at the left side of the pic.
VisoIII_LTM_2.jpg
3) The button to activate mirror movement is apparently unmodified; on the contrary, the lever to connect it to the body shutter releas button has been completely removed, with a black screw to cover the hole: it was obviously unuseful, for it is dimensioned for BM bodies; so, differently from the Viso modified for the Leica CL body (thanks again JC...
) they have decided not to make a custom lever to "reach" the LTM body shutter button.
VisoIII_LTM_3.jpg
My conclusion is that it is a very interesting item, I think custom modified but probably not at Leitz factory : it's a well done mech work that, for instance, a good repair lab can execute easily and with small risk : you haven't strict tolerancing problems that can, say, put at risk correct focusing... the Viso is a reflex device and, whichever the optical gear you mount in front, it shall surely have some focusing adjusting (bellows-like or screw-like). The "user environment" ? I'd bet tech/science... medical, probably, or even astronomy... The price is high but not exaggerate: for a collector of "Leitz strangeries" can be a good buy.