I do think it is a fun gimmick, definitely something that catches my interest, and I have considered buying a box in the past.
But I feel like with something like this you have to be careful, because you quite literally don't know what you could get.
For example, a youtuber I watch, Grav3yard Girl, A.K.A Bunny, recently bought a 90's themed mystery box, was totally excited and then all her hopes and dreams came crashing down around her (too dramatic?) when upon opening this box that cost $950 dollars, it was not filled with 90's memorabilia like the listing description promised but was instead filled with old thrift shop wind-breakers, a doll, an old hair-dryer, tons of little plastic gumball-machine helmets, a beanie-baby that possibly had a bedbug on it? as well as mold or actual feces on it, some kind of slime-esque "toy" that had MOLD on it, as well as other items, most of the items not even being from the 90's.
Basically instead of getting a legit 90's box, she got a health-risk.
The description was even 100 % misleading,
"Huge Box filled with tons of 90s memorabilia. This box will have tons of value and brings back all the 90s glory. Don't miss out; trust me as a 90s kid that was a major collector this is a treasure trove. No duds.
Box items will exceed purchase price. "
"Believe me you can not even guess the the contents of this mystery; it will bring wonder, joy, laughs and confusion. Guaranteed to be the Worlds Weirdest mystery to uncover; join all your friends around for Hours of laughs and confusion with this boxes surprises in which their are a plethora."He uses pictures like the above so you don't even know what the box is going to look like (which could be ok with some people, but his box was dirty and filled with questionable items that posed a risk to not only her health but possibly the health of her boyfriend as well, so IMO, I would prefer the listing show the actual box you'd be getting). He's definitely not the only one who does this, but he is definitely an example of the kind of people you should be wary of when looking for a mystery box to buy.
Tons of people are getting in on this craze and tons of people are potentially getting ripped off. Granted, most scammy mystery boxes will probably not be aimed at you the way his was aimed at Bunny (again, could just be speculation, just a thought). He targeted her using what she was looking for, gave it a price that suggested it was filled with tons of great and legit 90's collectibles as well as a description that misleadingly promised that that would definitely be the case, and, unfortunately, it paid off for him, and hopefully she will be able to get her money back, should she decide to try.
I am not against mystery boxes, this is a fun concept, one that I would actually like to partake in and make my own mystery box to sell (though because of people like him, it's now impossible and has been ruined), but when you are looking into buying a mystery box, pay attention to the pictures, as well as the details on the listing. There are people who include as much as they can about the box without spoiling the mystery and fun of it, but enough to let you know you won't be getting ripped off, or fucked over, or scammed. There are also people who don't necessarily share that much information but ensure that there is no junk without making specific and misleading promises about the contents. Again, personally, I would really only look into mystery boxes that show you an actual picture of the box you'll be receiving.
I also would recommend not spending tons of money on this sort of thing. I, personally, would never spend more than 50 dollars on a mystery box.
Like with anything you buy on eBay, really look over the listing, if you have questions, ask the seller. Try to get as much info as you can before you buy something especially if its a blind box or mystery box.