I've worked with several CMR cast resin locomotive shells, the biggest problem they've had (and still do) is that you can't cast or print handrails. Well, that's turned into a nice little sideline for me this year, I think I've done about a dozen or so soldered brass handrails. The only thing I've seen with those is most are clearly knockoffs of somebody else's shell as a master, and the resin shrinks just a hair, making it difficult to get them back on a stock frame without some modification of something. But surfaces are excellent and the end results equal to any styrene shell.
The RP printed FUD resolution has greatly improved from Shapeways, but man, that stuff is BRITTLE, it's like working with glass. But too many designers have made no attempt to design to a functional mechanism, and if you're trying to 'fix' one to fit a frame, good luck.
I've had several printed resin shells too, some with warping, some equally brittle, and a memorable print of an EMD engine block that reminded me of a Rollo candy, all soft in the middle, completely liquid.
I know with mine I've stuck with my cast resin after an experiment with Shapeways, quality wasn't bad but you can't make any money that way, it's an exercise in ego-building. My son has gotten quite good in resin printing, but his cost factors are really high and he's on his third printer, with hundreds of hours of modifications and tuning to get the good results he has.
80% of the cost in my kits isn't the shell, it's the photoetched metal detail parts, and you can print anything you want and you still need those.
CMR decals have been a mixed bag, good print and color quality, but to get a 'white' or light-colored decal they really pile on the layers to the point it's a battle to get them to seat (bubbles, wrinkles, or just falling off), but only on a stripe or a wide section, usually not lettering. I had to have several sets redone by them.
I just got a printed resin 85' ATSF mail container car that is truly a BIG resin print, and the containers were printed solid as part of the car they are on. I was skeptical about possible internal curing or warpage issues, but it came really well done. So it can be done, and done right.
