My 590 (8+1) arrived exactly as the shotgun pictured within the link you provided.
Since then, I have "converted" it to a 590A1 by replacing the heat shield barrel with a heavy walled one, the trigger assembly with an all metal setup (although, this is not really necessary..but, I felt it provided a better "feel" vs the standard plastic configuration) and the plastic safety w/a metal one (definately the most important "upgrade" out of the 3). In addition to all of this, I swapped the original front bead w/a Meprolight tritium unit.
While I did like the look of the heat shield barrel, I preferred having the structural integrity the HW barrel provides (even though it probably isnt really an issue). Regardless, since this SG is mainly for HD use and is my most often fired shotgun, I felt the stronger barrel justified a bit of additional weight. The heat shield barrel is now in storage...as a backup if needed.
One thing to note, sometimes these Mossberg guns have issues w/the stock mag tube spring/follower. I experienced this firsthand on my first outing with the gun. However, upon replacing the stock spring with a Wolff "generic" spring (which you can cut/fit yourself) and a Vang Comp follower, I have had no issues whatsoever. Regardless of whether you go with a 500 or 590, I would strongly suggest upgrading the spring and follower...if nothing else.
Now, one more thing I noticed, I was getting a bit of snag while directly feeding ammo into the tube. It turned out that the elevator needed a bit of polishing in order to smooth things out. No problem. A bit of fine grit sandpaper and a few minutes took care of this.
After a bit of "tweaking," I can honestly say that for me, even when compared to my Benelli SuperNova Tactical, this 590 is a SG I have total confidence in and do not regret buying one bit. To tell you the truth, the only thing I regret is not buying a 590A1 right from the start. At least where I buy my weapons at, the cost differential between the "standard" 590 vs. the 590A1 is nominal at best.
After all is said and done, I would opt for the 590A1 if I were you. But, if you insist on the 500, well...thats not a bad choice either.
Either way, the main reason(s) I went with the 590 would be as follows: 1. stronger, more useful feature-set vs. the 500 and 2. the safety location (as compared to most other shotguns). To comment on this last point- I dont care what anyone will tell you, IMHO, having the safety button located on top of the receiver is faster and provides much quicker feedback, in terms of safety status, than the "usual" setup ever could. At least for HD purposes, this alone is worth its weight in gold.