With the familiar disclaimer that I am not a lawyer, I will add that this set in particular is skirting a very fine line, if not crossing it. In the U.S. at least. It certainly shares a very strong resemblance to the Alien Chestburster, which as noted above was designed and created by the artist HR Giger for the movie, originally owned by 21st Century Fox I believe and now Disney. Copyrights for graphic characters (which this would fall under as a primarily visual character and recognisable by distinctive visual characteristics) are good for a minimum 50 years, if it is trademarked this can be renewed indefinitely (trademark and copyright are different yes, but share many of the same legal characteristics, as has been seen over the past 20 years). There are many ins and outs to copyright law, again I'm not a lawyer, but in my work copyrights, reproduction rights and licensing are something we deal with frequently. People like to use concrete terms when it comes to copyright but in the end it doesn't matter if you sell/use something as an "outer space bug" as opposed to "Alien Chestburster", or change a minor aspect of it's appearance, there is no guarantee that this is enough differentiation to avoid litigation. In the end it is up to a judge to determine if something is infringing on a copyright. In copyright law for visual designs and products this has to do with a combination of factors that are examined; appearance, context, character traits, and of course, precedence. I'm certainly no expert but based on my dealings I would highly recommend any retailer stay away from selling this product, especially with Disney as the new copyright holders.
Its one thing for the Arvo bros to sell it on their own website, it's likely not worth the legal expense for Disney to pursue, but if a large organized company (for instance a company in a position to challenge LEGO's market position) is using this likeness to make money without permission (and maybe they do have permission for all I know) it is only a matter of time. And while a small outfit may get a cease and desist as a warning, a larger company likely would not, especially if the copyright holder thinks they are making any decent sum of money or are using the copyrighted material in a way the copyright holder does not approve of. And no, the offender would not get thrown in jail, but they could be charged a hefty sum and face other civil consequences depending on the circumstances. Its important to note the difference in selling instructions vs. sets the way most independent moc designers do, as this does change things and moves copyright into an even grayer area, here simply changing to a non trademarked name might be enough, it's a bit harder to say definitively. But when larger companies get involved with this it is very problematic, it's easy to say what's the big deal it's just big bad Disney but imagine if LEGO published an original design of a distinctive character by a moc designer, changed a few bricks and the name of the character with no credit to the designer then you begin to see why. Of course in fact this does happen all the time, unfortunately independent designers and artists frequently don't have the resources to take big companies to court, which in a perverse way is why it is all the more important for these large copyright holders to fight these things because they are often the only ones who can.
In any event its certainly not ethical and likely not legal.
Edit:.If you made it through that wall of text, congats lol.