I use RP shops a lot and unless you plan on going into business making RP parts, shop it out. The machines change enough over the years that you will be stuck with a low resolution machine if you are trying to do it on a budget. Same goes with 3D scanners. They change so much it isn't feasible to purchase one unless that is your business.
Prototypes have evolved a lot in the last ten years. The last assemblies I did were full functional prototypes for a large consumer electronics company. I had crystal clear buttons, LCD screens and tuned micro speaker housing. Next to the competition, you couldn't tell that it was a prototype other than it didn't have knit lines like the injection molded parts did.
As for strength and real world application... yes, production parts are made on these machines. The main shop I use makes MANY parts for the Boeing 787, FA-18 Hornet and the Osprey. They are all FAA certified and going into production aircraft. The blends they have today are light years ahead of anything that was available even three years ago. There is even a special carbon composite material I was able to see that is simply amazing. Not cheap, but VERY functional in high performance applications!
As for it not being able to replace CNC metal... these are parts that simply cannot be machined nor molded due to complex geometry. The ONLY way to make these as single parts is to build them in the RP machines. One of the 787 components for example replaced 17 separate injection molded parts with a single RP part. Amazing!
Mikado USA, Kontronik, Opti-Power, MKS Servos