I have used red dots over the years. On mil specs Aimpoints and Eotecs, but on my Marlin Lever I have used a Athlon and currently, Vortex Venom. I like them a lot for short to mid range snap type shooting. They are very quick to acquire and easy to use. Very effective once zeroed.
Dedicated red dots, as opposed to a scope with one in the reticle, seem to come in two basic types, a short tube type, see the aimpoint micro (V expensive) and the type with a stand up window. I have the latter on my Marlin right now.
I tend to use a 2 moa dot. Seems a good compromise where smaller can be hard to see, especially on bright days and larger becomes harder to be accurate with at longer ranges. A 3 moa dot is also fine.
Red dot sights can be cheap and good these days. I would suggest starting around the $100.00 mark, though many are available for less.
Footnote, some people have trouble seeing the dot clearly. They have astigmatism and see a flare or distorted splodge. This doesnt prevent them from using them but can do. Depends on what they see, how distorted. A good trick I was told was to take a picture of the dot with a phone camera and compare it with what you see with your Mk1 eyeball.