There are a number of variations, though you wouldn't know by OFM's new web site.
Just about any imaginable configuration with either a 20" or 18 1/2" barrel. The shorter barreled guns will have a 5 round magazine and 20" guns have an 8 round magazine.
There are heatshields, adjustable stocks, stocks that hold more rouns, sets that include a bayonet, ghost ring sights/ either LPA or OFM factory, rifle sights, bead sights, railed forends and standard ribbed forends. The A1's will always have the extra metal parts and heavy profile barrel. What do these add? These were added to the design at the specific request of the US Navy as I understand. These things are intended to beef up the design to prevent damage due to bein repeatedly knocked around. I also have a couple 500's and have yet to break any of these pieces in plastic form. Still love my A1!!!
The light is def an aftermarket part. Before you buy, you may wanna look up that specific model number and seethe MSRP at least. Now if it isn't that important and you like it just the way it is then go for it! Its worth whatever its worth to you!
Oh! The light! Yes it can give you away. It isn't meant to navigate, ID and make a split decision. That's how I view it. Friend or foe, then decide what needs to happen. It may sound weird but I know I'm not alone when I say I practice clearing my house. With practice, your brain processes and decides what to do way faster than we can describe or read it here. If you use a light and decide. To illuminate a target, you either recognize the target or decide its a threat and elimiate it. If its a threat to my family, to my wife and children, I see no reason to hesitate so I don't worry about giving away my position. That and everyone I know, knows not to let themselves into my home in the midle of the night.