Here's what I know about the single point sight...
They were at least 2 types of red dot (day & night type) and at least 1 type of light green dot.
Some had rounded ends & some were squared off (I think the squared off type are night versions)
They are known as OEG's - OEG stands for Occluded Eye Gunsight. That means that one eye is blocked from viewing the target. You must have binocular vision for an OEG to work (some people don't). Basically one eye sees the red dot in the sight and the other eye sees the target. Binocular vision lets you see both at once, superimposing the image of the red dot on the target.
They have an interesting history being used in the Son Tay raid to rescue american POW's held in North Vietnam..."In 1970 whilst training for the raid, Col. Arthur "Bull" Simmons was unhappy that even his best shooters were getting only about 25% of the rounds fired at 50 metres into torso-sized targets. This was'nt too clever when the expectation was to bring down the opponents with single well-aimed shots to avoid hitting the POW's. the story goes that one night Simons and his armorer were trying to solve the problem when they came across an ad for the Single Point OEG in Guns and Ammo. They ordered the nite versions and the results were amazing - even the poorest shooter could put all his rounds inside a 12" circle at 25m. with both eyes open, men could shift their fire from one target to another just as rapidly as daytime and with the same accuracy - the supply guys then went an bought enough to equip every raider with the sights"
http://img11.photobucket.com/albums/...669/Slide8.jpg
Here is a pic from the JFK Special Warfare Center Museum of an original Singlepoint in the mount:
http://www.usmilitaryknives.com/Son_Tay_raiderequip.jpg
Values seem to be about £50 for a nice example with no crimping, intact dust covers and no cracks or milkiness in the front end.
(I believe they are quite sought after in the US with vietnam collectors to put on thier M16's)
If anyone has any orginal advertising info. - I'd love to see it.......