I've built up a couple of 870's so, FWIW: The Speedfeed stock holds two rounds, on the lower, inboard side of the stock, in a spring-loaded channel, the shells are retained by a rib, at the mouth of the channel. Two more rounds are held, off-side, parallel to the comb of the stock. I never found it particularly "fast", the chief advantage being that you didn't have something else hanging off the gun to snag. For speed, I prefer the reciever mounted carriers, and for quantity, back that up with a butt-stock, nylon, carrier (Eagle, Blackhawk, etc), with a closing pouch.
Ghost-rings- I really like them! If Bro/Sis are bird hunters, they may not. If he/she isn't, and they practice swinging-to-target with the GRs(trap and skeet is hell to practice with these 18" barrels!), they will probably appreciate them. Again, if they're hunters, stick with the bead, they'll maintain their personal comfort-zone, and speed.
The two more rounds offered by the SS model. Well, you can spend $250 or so, for an Express, and +/-$40 for Scattergun Technology's tube extension, and try it both ways. If they/you think you might like the ghost-ring option, my favorite has alway been MMC's- easiest to adjust, low profile, and built like a brick poop-shed. +/- $120 or so.
You probably will get a smoother, somewhat more "industrial" build with the CDNN shotgun, but you need to weigh that against the intended user's ability to utilize and appreciate that. Unless you
know that you want the SS features, I'd go basic, and build from there.
http://www.mmcsight.com/shotgun.htm
http://www.wilsoncombat.com/index_sgt.htm
http://www.eagleindustries.com (They used to offer this with a full pouch- might be worth calling- SSSC-QTR is the product code)
http://www.speedfeedinc.com/?location=products (The Speedfeed I Mag Tube Stock Set)