could be express v. 870P ... ?
Are there constructional differences in the $499 870 that the Synthetic does not have?
RTFM, I can't see the images well enough to answer that with any kind of confidence, so take this with a huge grain of salt until someone more knowledgeable than me responds.
It could be (just a guess here) that the more expensive "tactical" one is based on an 870 Police model (870P), where as the less expensive one is built on the Express. (Added by edit: if so, then there should be different designations printed on the receiver of the one at Sportsman's Warehouse indicating it's a P and not an Express...I think...again, take with salt...)
If that's the case, then yes, IMO, it is worth the difference in price.
I explored the differences between 870P's, wingmasters & express
ad naseum on THR before buying my 870P. I paid ~$150 more for the P, but IMO, it was worth it.
Others will have better knowledge of those guns you're looking at, however.
Nem