I have copied and pasted this text from a thread I did a few years ago when I built a resin kit from Iconicair. I've re-read it, and there is nothing in it which I would change today.
"A word about 'resin'. What we all call resin is just another plastic, almost invariably polyurethane. You will read all sorts of stuff about it which might lead you to think it's as dangerous as asbestos and will have the same effect on you as kryptonite on superman. This is a load of tosh. I am not talking about working with the chemicals mixed to create the plastic, for which different precautions would be required, but working with polyurethane parts.
First, you are not going to be gassed by the parts (yes, I've actually read that you can be on one forum). Any out gassing going on (if it is) when you get the parts is minimal and not dangerous.
Second the dust is not a material so hazardous that it will almost certainly destroy your lungs within seconds of exposure.
The dust, like just about any other dust, is not good for you and you should take precautions to avoid inhaling it. You do not need a Darth Vaderish mask of the sort I wear to protect myself from solvents etc when I spray paints and lacquers, but if you are producing a lot of dust then a suitable dust mask is a good idea. You can minimise the dust you produce by wet sanding, not exactly rocket science! I also minimise the level of dust in my work area by vacuuming up any deposits fairly regularly, being careful not to vacuum up kit parts.
Really this is nothing you shouldn't do when sanding wood and certainly things like car body filler or fibre glass (which really is nasty stuff). It's just common sense.
There is no reason to be frightened of working with resin. It is an easily worked plastic, easy to cut and sand, and works well with CA glues (superglue) and epoxy resins. The fit of resin parts, how ever well made, won't be as good as injected polystyrene parts and this is due to the way resin shrinks as it hardens. This is one area where there will almost certainly be a bit of work to be done. Cleaning parts up is no more difficult than cleaning polystyrene parts. I use the same general tools, good knives, razor saws, files and wet 'n' dry, all of which most of us will have in the tool draw.
I'm not suggesting everyone should go out and buy a resin kit, I think a bit of experience is a sensible prerequisite, but nobody should be put off by a kit with some resin parts nor should they be scared to take a swing at a resin upgrade set or similar."
You can certainly produce good models from resin kits, but you will probably have to work a bit harder at it than some, particularly newer, injection molded kits. That Iconicair kit made this Seafang.
Cheers
Steve