Well, I've always thought the Magpul 870 stocks were ugly (the forends look good IMO...) but the flat dark earth version is a little more aesthetically pleasing than the rest; at least to me. Here's a run down of the pros and cons for the stock and forend:
Stock
Pros:
-12.5''-14.5'' adjustable LOP
-Very easy to install
-I find the grip angle very ergonomic
-The fit with the receiver is great
-The grip area allows for better retention in the event of a gun grab attempt
-Adjustable cheek risers for use with optics availible
-A couple different options to attach slings
-Standard 870 recoil pads can be used with the stock (requires an additional Magpul adaptor)
Cons:
-Cost (anywhere from $85-100)
-It's ugly looking
-Only available for Remington 870s at the moment; Magpul says the Mossberg versions are in the works
Forend
Pros:
-Cost (between $25-35 most places)
-Ease of installation
-Modularity (slots accept standard Magpul rails and accessories)
-Very solid fit; no wobble like some forends
-The built in handstop really helps you get a positive grip to run the gun hard even with sweaty hands
-Looks good
Cons:
-Creates wear marks on the barrel/mag tube (doesn't bother me but it may bother some)
Here's a video of me shooting my 870P with the SGA furniture and discussing some of the pros and cons of the setup:
MAGPUL 870 FDE SGA ACCESSORIES HD VIDEO REVIEW LINK
