It is anything than reasonable to assume that the VEPR is legal in a locality because someone is selling one in it. Even if it is legal where it is for sale, what if the person wants to bring it on trips to another jurisdiction or moves to it? It isn't at all unusual for someone to learn that, while previously they were not aware of the offense, that they were in possession of what was clearly deemed by their state to be an assault weapon and that they were chargeable with a felony.
As I stated several times previously in this thread, always know your local rules and regulations.
How many detachable box magazines semi-automatic shotguns are there?
Not many.
The VEPR (which are quickly drying up on the new market), the Saigas (which have dried up), various Chinese Saiga clones, the Chinese SAS12, the various Turkish AR-lookalikes (that are loosely based on the Remington 1100 action), and some others. The VEPRs are generally considered to be the best of these. The Saigas were well-regarded, but the VEPRs are a step above in terms of durability and finish (but still an AK derivative, so make of that what you will).
IMHO, there's a reason there aren't many of them, and that's because the market has determined they are a technical and practical dead-end (for multiple reasons).
So all of our exchanges are meaningless. Would I buy a Vepr shotgun, no
way I can think of better things to waste my money on.
No disrespect intended, but the "meaningless" posts were those that brought up trap shooting and high-end sporting guns. The OP was in no way asking about that. He was asking for information about and comparisons of two specific models.
And, as far as the subjective wasting of money goes, there's all kinds of ways to do that, including breaking little clay discs in the air. It's best not to look at leisure activities though the lens of financial payback. You'll almost always lose. Their value comes in other forms - psychological, stress relief, alleviation of boredom, making of positive memories, etc.
As I said earlier, if this shotgun is meant as a serious-use defensive shotgun, the 590A1 would be my choice over the VEPR hands-down. It's generally going to be more reliable, have a better ratio of capacity to size/utility, be lighter, more ergonomic, easier to handle, and easier to service and maintain.
If it's just a fun gun, or something to fill out one's collection, then all bets are off.
Unless the OP returns to elaborate on his intended use, there's really not much more to add here.
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With 2.75 inch shells, the Mossberg has a capacity of 8+1 and the Vepr has 5+1. I'd say in either case, that will probably be enough for a home defense situation. If you are buying the shotgun for some other reason or think you'll burn through more than 8 or 9 rounds in a home defense situation, then the Vepr may be a better option. Cost wise, you should be able to get the Mossberg for around 300 dollars cheaper.