I've been playing with a low-end Simmons red dot sight. I've never had any experience with these type sights and I thought it was time to get acquainted. The price was certainly right, under $40.00 at Midway USA.

I mounted it on a Remington Model 760 pump action rifle in .30-06. .30-06 is a fairly serious caliber, a benchmark of rifle cartridges. I wanted to test the sight against recoil with a common cartridge. It has held up well so far, with the sight holding zero after a hundred or so rounds of ammunition.
This is not a scope, it's a sight. It is not designed for precision work, but for quickly shooting at targets of opportunity. The red dot subtends 5 minutes of angle, which is 5" at 100 yards. The sight has 11 settings for brightness on the rheostat, which makes the sight useful during bright sunshine and during total darkness.
Using the sight on a police range, I was routinely able to make head shots at 50 yards on a man-sized silhouette. I had the rangemaster turn the target away, then present it for two seconds. I put the rifle at the low ready position and when the target presented itself, I came to the offhand unsupported position and fired one round. Head shots were easy in the time allowed. Two seconds. The target reset after two seconds. If I had tried this at 100 yards, I'm confident that the shot would be successful.
This isn't a precision scope. It is a quick sight. The red dot presents itself against the optical plane and once adjusted for the ammo used, it is a simple matter to place the dot on the target and squeeze the trigger. It is very fast.
Parallax, you ask? Oh, there's plenty. The red dot moves around as you look through the sight, but your brain (that magnificent ballistic computer between your ears) tries to center the red dot through the sight. I suspect that at 100 yards, it might have as much as 24 or 36 inches of parallax, so I took some photos to show how the sight works.

Here's a photo through the sight. The red dot is out of center and is high in the sight. It appears against the base of the tree in my neighbors yard.

This photo shows the sight out of alignment with the red dot at 8:00, almost out of view. The red dot is nearly obscured by the body of the sight, yet it is still on the base of the tree.

Here, the dot is low in the scope, yet it still presents against the base of the tree. The rifle wasn't moved as I shot this series. I took these photos against a stationary rifle. I feel confident that if I had to engage that tree, the bullet would have hit the target, even if I didn't center the sight in the picture.
However, our brains try to automatically center a dot in a circle. So, a quick movement, the dot would center and the shot would be made. It takes longer to write about it than to do it, and I find this sight to be extremely fast.
This sight would probably be just the ticket for fast snap-shooting at short range, in a still hunting scenario where the targets present themselves quickly. It doesn't take the place of a good scope, and shouldn't be interpreted to be the best sight for deliberate, long range fire. However, many times shots present themselves at ranges under 125 yards and this sight might be useful at the beginning and end of the hunting day, and in deep woods where a front sight isn't always visible.
There is the problem of batteries, though. I'm still using the original that came with the sight, but I'm careful to turn the sight off when I'm not carrying the rifle. Good practice would probably demand that I obtain a couple of spare batteries before hunting season.