We just upgraded our cruiser shotguns from bone-stock 870s to ubertactical ninja guns (thats my PD, baby. Blazing a trail into the late 1980s today!). We took the standard, out of box 870 with 18" bbl and did the following:
1. Added a Surefire forearm
2. Added an extended magazine tube (2 shots)
3. Added a Speedfeed PG buttstock
4. Added an Uncle Mike's Tactical Sling
The only modification that I think was at all
needed was the Surefire. The rest definately fits in the 'nice to have' category, but it is foam on the top of the beer and nothing more.
Why?
Well, the extended magazine tube adds weight and changes the feel of the weapon...two things that are not necessarily bad, but that you need to address in training. And 4 shots is likely plenty to have ready on tap. The other 2 are nice to have, but probably not absolutely necessary.
The Speedfeed buttstock is a PITA. I disliked the PG, but I'm now used to it. Getting the shells out of the stock tubes, however, is hit or miss. Sometimes they just want to pop right out, other times you have to dig and claw at them. Not good in a fumble-fingered adrenaline-thumping jeeze-I-need-a-slug-right-NOW scenario. A
good buttcuff is probably better.
The tactical sling is a good idea for anyone who might be doing urban assault ninja ops, but for a lock-yourself-in-the-bedroom-and-call-911 usage, the most it is gonna do for you is get hung-up on the bedpost and slow you down.
Most importantly, if you get a forearm light, I DO recommend the Surefire. Yes, they're pricey. But they are rock solid and they work. You CAN find them places for less than MSRP.
www.lagger-pro.com is one, and the dreaded
www.botachtactical.com is another. For HD work, the smallest/cheapest one they have (6v?, touch-pad) will work just fine.
Mike