I like the look of two-tone polymer guns... I have my .45 PX4 being cera-plated by CCR. Personally, I'd recommend them.
Cera-plate and NP3 are pretty similar. I did a lot of looking on SIG Forum, being CCR is pretty big there. A lot of people say that cera-plate is better than NP3, due to it not being as slick. That was a big thing for me.
The second thing was cost. For $379, I am having my pistol and seven magazines plated (the frame will be completely disassembled, and the only things not plated will be polymer parts and the extractor). I'm also having a Stealth decocker and Trijicon sights installed, as well as night sights being added to another slide. That is also shipping it back to me...
After taking a look at Robar's pricing, I would be paying somewhere in the neighborhood of $500. I say neighborhood, being I'm not sure how they would handle a larger job like mine. Still, if they do consolidate some costs considering what I want to have done, they are not getting into the $379 range.
Now, if I was looking to have the polymer frame modified, I may have paid the extra to send it to Robar. Not sure. All I know is that my past experience with CCR was great, and I really can't see a way that Robar could improve (well, maybe turning it around quicker, but I rather wait for something to be done right).