I had them make some .338LM Improved 40 brass for me based on my reamer print. Yeah, it's pricey, but the quality is outstanding and in my case eliminated my need to fireform for in the first place. The only problem I ran into is that I had to ream all of the primer pockets because they were too tight.
If quality brass is already available for the cartridge you want, I'd stick with that. But if you're shooting a wildcat or something where quality brass is non-existent, then definitely go the RCC route. Mine took a good six months and I got mine during a big sale at the start of the pandemic, which took some of the sting out of the price.