C-More Railway is a World Champion Sight used on more Open Class Race Pistols than any other red dot reflex style sight...and for good reasons.Also an effective rifle sightThe housing may be longer than most red dots but that gives the laser beam a significantly longer distance to travel between the diode module and the splitter lens which results in more accuracy for the shooter.Most other red dots also have only one "cross bolt" for mounting which may result in side to side wobble and resulting inaccuracy...Not only does the C-More Railway have 2 mounting "cross bolts" but the rear cross bolt slides fore and aft to allow more mounting options. Also of HUGE BENEFIT...the C-More Railway works on most Picatinny (MIL-Std 1913) AND Weaver Rails. This sliding rear mount facilitates use on " factory" rails which may have intermittent cross slots like Rugar 10/22 rifles or Browning Buckmark pistols. It is possible to purchase and install a third cross mount for really large caliber applications.Keep in mind that position 1 and 2 on the click switch (for intensity) model are for night vision optics and you will not see a red dot in either of these positions unless you are using night vision...there is nothing wrong with your unit.Do not dismay about buying the Polymer body...most semi-auto pistols are Polymer bodied and this is just as "beefy" in the hands as they are...there is a sense of high build quality when you hold/operate the Railway.The Polymer model comes with an extra set of battery cover screws and 3 wrenches...the aluminum body comes with extra screws and 2 wrenches.Uses a 3 volt lithium battery-Duracell DL1/3N or Energizer 2L76Diode modules are available in six different sizes-2/4/6/8/12/16 MOA if you need more than one red dot size at extra cost of courseThe 8 MOA is a good starter size for pistol useSee this link for a factory chart which will assist you in choosing the MOA Dot size you want..http://www.cmore.com/diode.htmlThis unit will co-witness with some higher fixed factory sights.C-More makes the same unit for direct mounting applications and co-witnessing on low mounted fixed factory sights.If you want to direct mount-the Railway IS NOT the model you want...look up the model...Slide Ride. It is basically the same optic minus the mounting railway and because it sits lower via direct mounting to the weapon without a rail...it will co-witness with lower mounted fixed factory sights. To be clear...to direct mount, your weapon will need to be or already is drilled and tapped for optic/accessory mounting.While this unit seems huge, in hand it's smaller than you thought it was going to be...When you are ready to buy you need to decide the following in this order:Railway or Sled RideAluminum or PolymerIf Polymer...what color...aluminum comes in black only (darn...aluminum can be anodized in colors C-More!!!)MOA Dot SizeA bit of a labor intensive shopping experience that results in a really high quality reflex red dot optic purchase....I liken it to picking car options...remember when you could do that...LOL