1. click "quote reply" instead of "reply" and it shows who you are responding to
2. lots of low price RedDots on Amazon (cheap is good, on a camera they don't need to be able to resist the recoil of a rifle or shotgun) I have two, an AIM and a Vokul. These two and a bunch of others look alike and probably come out of the same factory in China. Prices range from $10 (Crosman) up to hundreds of dollars for Military Spec sights. They usually have a choice of shapes for the aiming point and color choice for the aiming point, usually red or green. The first ones were all red and only had a dot aiming point so the name Red Dot.
http://www.amazon.com/s/ref=sr_nr_p_6_2?fst=as%3Aoff&rh=n%3A3375251%2Cn%3A10971181011%2Cn%3A706813011%2Cn%3A13364359011%2Cn%3A13364369011%2Cn%3A4200781%2Cn%3A3226129011%2Ck% 3ARed+Dot+sight&keywords=Red+Dot+sight&ie=UTF8&qid=1484430166

3. They are made to fit on a rail attachment point on a gun so you need an adaptor to go on the hotshoe. (Every so often someone will offer a sight made for hot shoes, but they are hard to find and often over priced. Here is one with sight and adapter for $59 - http://www.amazon.com/AstroStreet-Optical-Adapter-Camera-Reticles/dp/B01C5W2EFE/ref=sr_1_1?ie=UTF8&qid=1484430837&sr=8-1&keywords=red+dot+sight+to+hotshoe+adapter) They sometimes have others, as cheap as $10 on Amazon.
But the Camera Cottage, owned by MT Shooter here on the UHH has a photo quality one with a long mount to allow adjustment for eye relief for $29.95. http://www.cameracottage.com/apps/webstore/products/show/6655934 It is a new product, I have one, the other adapter you see in the picture is one I got over two years ago on Amazon, the company seems to have disappeared since. He is also the US distributor for the Nest Gimbal head and has a variety of their tripods.

One of the advantages when trying to find a BIF or similar in a hurry, you don't have to have your eye lined perfectly with the sight all the time. If you are say 25 yards from a perch visited by your subject frequently you adjust the sight for that range and as long as you see the "dot" you will have your center point close to the subject, at that range and a bit closer or further away. Just sit your zoom to have a bit of extra in the picture and you can crop later. If you have fast reflexes and good coordination you can switch to the viewfinder to check and back to the Red Dot for following a moving subject. With a still subject once you find it in the Red Dot then you just go to the viewfinder. Astrophotographers also often use Red Dots to avoid hunting all over the sky with a long telephoto to find things.