I bought a SightMark reflex (not red dot) sight at Cabelas a while back for my Colt M-4 .22. This is the first reflex sight I've had. It has 5 brightness settings for the aiming spot, all noticeably brighter than the last. On the gun, in the house, any of the brightness settings were perfectly visible. However when I took it to the range, in broad daylight but under a roof cover, the aiming spot was completely invisible even at the brightest setting. With close inspection you could see that it was actually there but completely useless for aiming. I have returned it to the store but I got to wondering if this was normal? Doesn't seem like it should be but I've never had one before?
With optics you get what you pay for, the Sightmark reflex is very inexpensive the better reflex sights are 5-10 times the price, the only difference between the two brands is the more expensive sights actually work!
Agree with BSB;
Some sights, including some top end models, are hard to see in daylight. I've played with an Eotech on an M4, in daylight, and was less than impressed. My Bushy M4 wears an Aimpoint Comp M2 series sight system.
It was not cheap, but works well day or night, and even has the ability to be used with NV. It is co-witnessed with the M4 front sight and the mounts are rock solid.
Sorry you have had a sour experience. Perhaps moving to a red dot style might be the way to go if you are so inclined? The top end sightmark is only say 50 or so dollars less than entry level red dots.
Whatever you decide to do, make sure that the sight option co-witnesses with your irons, even if they are the fold down option style.