The cone type were the earlier and were sold to the military. They are collectable due to the POW rescue mission, but only in the US. Militarily they never did that well, as iron sights are about as good in good hands.
The civilian, hunting, version was pushed hard though rather than for running boar they found a niche with AGW air gun plinkers. And then as they were "space age" as Star Wars props; they were pretty cheap.
That the "dot" isn't exactly small they at best are fair for farmyard ranges. They are reasonably quick, but parallax issues and needing to be sighted to the individual, don't make them that accurate. Solid hit on target rather than precision.
Quite fun though.

The Sussex Armoury air rifle ones first came with a one piece front mount. These could crack the perspex if over tightened!!! They did look cool though. Many were mounted with two piece, usually fairly cheap ones of the time. Two piece were better, but often leave mount marks in the paint finish.

There were also barrel fibre optics beed sights for shotguns.

I've had at least ten Single Points over the years; two I sold at Star Wars prices. I buy any I find cheap.
There were two types of turret cap, rubber and metal. The thread to the metal type was short and poor so many were lost. The rubber ones weren't much good either.