We have sold quite a few of the 3 barrel 535's (and I think you mis-stated the model unless they did them up in the Mod 500 as well). This was a special from Mossberg that is now discontinued (but there are some flopping around).
The 535's will fire 2 3/4", 3" OR 3 1/2" shells and as noted includes a 28" VR, a 24" Turkey choked (extended choke) plus a fully rifled deer barrel with a cantilever to mount a scope - plus there is three choke tubes (I/C, M and F) for the VR barrel.
The whole shebang can usually be had for somewhat under 600 bucks.
For 2015 the 870 Express Supermag in Camo (so we are comparing apples to apples here) is coming in at the same price - and that's with ONE barrel (28" VR) and ONE choke (comes with a modified).
If you add the two additional barrels plus two more chokes, you are looking at dropping close to a grand for the "same package".
I am an 870 fan (own one), but if I was buying "today" and one of the Mossberg packages was available it would be tough to turn down - it's probably the best "value" currently in the market.
(and if you actually saw this package in the model 500 but are interested in the 535 supermag version they are out there - I just ordered another dozen of the dwindling stock at the wholesaler)