The obvious con is that you need UV source for the resin to cure. If you're curing under pressure, the additional con is that you need an UV source capable of withstanding that pressure. Duh.
The less obvious con is that setting depends in UV light penetration into the resin which tends to stop the light itself. So UV resins are best used in thin coats. Most kinds of molds will stop the light from penetrating into the resin as well.
The difference between UV resin and regular resin is that the component responsible for curing is trapped in a chemical compound that releases it when treated with proper wavelength UV light (This component is also the reason why they are so expensive).
Because of this, you can have some interesting properties, like long pouring times, with fast setting on demand (hello touch screen smartphone glues), or being able to set the resin selectively, and wash away the rest of it (hello screen printing, pcb etching, 3d printing)
So, unless you have something specific in mind, this looks a lot like a solution in search of a problem.
Btw, don't ever use polyester resin if you can avoid it. It's leaking xylene throughout its whole lifetime, which is toxic and unnecessary. It also ruins silicone molds pretty reliably.