First, shotguns are great for point blank to medium range, have amazing stopping power, and are very versatile with loads, and the barrels can be switched out in seconds from a hunting length barrel to a home defense shorter length.
I own a "home defense" 12 gauge Remi 870 Express. My opinion of this shotgun is that it's near perfect. I've shot it many many times. My main complaints are really petty and can be corrected. It would be nice if it held more shells with a longer tube, and that can be corrected for under $30. I prefer the safety placement on the Mossberg better, but that's minor. I currently have a synthetic stock. If I were to make any changes to a factory shotgun, my first change would be to add a sidesaddle or tube extension for more shells, my second change would be to install a combo pistolgrip/full stock for control. Avoid a pure pistol grip because you'll lose accuracy and it'll be difficult to control as well. Shotguns are made to fire from the shoulder, not the hip like in movies.
While I do not own a Mossberg, it's also a great shotgun. It's safe to say that Mossberg 500 and Remington 870 and Win 1200/1300 are the most common and best choices for home defense, and both can be had for around $250 or less, particularly at Walmart (I just saw the Mossy for $200 and the Remi for $250). They are easy to accessorize with a sidesaddle (for more shells), a pistol grip or pistol/stock combo, and other accessories.
I recently saw a Mossberg (not the 500, but a different model) combo with a home defense barrel AND a hunting barrel for $200 at Big 5. I think that sale is over. If I were in the market for a shotgun, that would have been it. Have fun.